History in the United States
Purple loosestrife was introduced to the northeastern U.S. and Canada in the 1800s, for ornamental and medicinal uses. It is still widely sold as an ornamental, except in states such as Minnesota, Wisconsin, and Illinois where regulations now prohibit its sale, purchase and distribution.
History in the United States
General: Loosestrife Family (Lythraceae). Purple loosestrife is an erect perennial herb that grows up to 2.5 m tall, develops a strong taproot, and may have up to 50 stems arising from its base. Its 50 stems are four-angled and glabrous to pubescent. Its leaves are sessile, opposite or whorled, lanceolate (2-10 cm long and 5-15 mm wide), with rounded to cordate bases. Leaf margins are entire. Leaf surfaces are pubescent.
Each inflorescence is spike-like (1-4 dm long), and each plant may have numerous inflorescences. The calyx and corolla are fused to form a floral tube (also called a hypanthium) that is cylindrical (4-6 mm long), greenish, and 8-12 nerved. Typically the calyx lobes are narrow and thread-like, six in number, and less than half the length of the petals. The showy corolla (up to 2 cm across) is rose-purple and consists of five to seven petals. Twelve stamens are typical for each flower. Individual plants may have flowers of three different types classified according to stylar length as short, medium, and long. The short-styled type has long and medium length stamens, the medium type has long and short stamens, and the long-styled has medium to short stamens. The fruit is a capsule about 2 mm in diameter and 3-4 mm long with many small, ovoid dust-like seeds (< 1 mm long).
Mal et al., 1992, provide a detailed morphological description for L. salicaria. The authors also give details of the tristylous features of this species, as well as an account of its pollen structure and chromosome numbers. The plant’s habit, vegetative, and reproductive structures are illustrated with line drawings.
Other species of Lythrum that grow in the United States have 1-2 flowers in each leaf-like inflorescence bract and eight or fewer stamens compared to L. salicaria, which has more than two flowers per bract and typically twelve stamens per flower. Lythrum virgatum, another species introduced from Europe closely resembles L. salicaria, but differs in being glabrous (lacking plant hairs), and having narrow leaf bases. The latter two species interbreed freely producing fertile offspring, and some taxonomists (Rendall 1989) consider them to be a single species.
Distribution: Purple loosestrife is a hardy perennial herb with stunning spikes of purple flowers. A native of Eurasia, it was introduced to North America in the early 1800's where it first appeared in ballast heaps of eastern harbors (Stuckey 1980). Most likely seeds were transported as contaminants in the ballast or possibly attached to raw wool or sheep imported from Europe (Cole, 1926; Thompson et al., 1987).
The native range of L. salicaria is thought to extend from Great Britain to central Russia from near the 65th parallel to North Africa. It also occurs in Japan, Korea, and the northern Himalayan region. The species has been introduced to Australia, Tasmania, and New Zealand. Since its introduction to North America, this alien plant has spread rapidly into Canada, and throughout most of the United States where it has been reported from all states except Alaska, Florida, Louisiana, and South Carolina. Several factors have contributed to the spread of purple loosestrife such as its potential for rapid growth, its enormous reproductive capacity, lack of natural diseases or predators, its use as an ornamental, and for bee forage (Mal et al. 1992). For current U.S. distribution, please consult the Plant Profile page for this species on the PLANTS Web site.
purple loosestrife, spiked lythrum, salicaire, bouquet violet
This species is native throughout Europe and North Africa east through Turkey, Palestine and Lebanon to China, Japan and Korea. It has been introduced to North America and Australia where it can be extremely invasive. In Europe, it has been recorded from all countries except the Faroe Islands, Gibraltar (UK), Greek Aegean Islands, Crete, Cyprus, Iceland, Monaco, Azores, Madeira, Selvagens Islands, Russian Franz Josef Land and Novaya Zemlya, San Marino, Balearic Islands, Canary Islands and Svalbard and Jan Mayen (Norway).
Regularity: Regularly occurring
Regularity: Regularly occurring
More info for the term: marsh
Purple loosestrife occurs in all but 6 states of the continental United States . It is found along the Atlantic coast from North Carolina to Maine  and is scattered but spreading in the western United States . Purple loosestrife occurs most commonly in the United States in the Midwest and Northeast, corresponding closely with the geographic extent of the Wisconsin glaciation [81,125]. It is distributed across the southernmost tier of Canadian provinces from Newfoundland to British Columbia, with northern limits generally around 51Â° N . The greatest concentrations in Canada are in southwestern Quebec, southern Ontario, southern Manitoba, and in British Columbia's lower Fraser Valley . The Plants Database provides a map to purple loosestrife's distribution in the United States.
Considered native to Eurasia , purple loosestrife has a widespread circumpolar distribution throughout the northern hemisphere, except in extremely cold and arctic regions [111,129]. Although the precise origin of purple loosestrife colonization in North America is unknown, it was well established by the 1830s within coastal wetlands along the New England seaboard, having likely been introduced via ship ballast soil. Further introductions are thought to have occurred intentionally by early American horticulturalists. Initial spread of purple loosestrife into the interior of eastern North America occurred primarily via routes of maritime commerce, such as canals, rivers and the Great Lakes. Spread into the arid West appears to be closely related to development of irrigation systems within that region .
The following biogeographic classification systems are presented as a guide to demonstrate where purple loosestrife could potentially be found based on reported occurrence and on biological tolerance to factors likely to limit its distribution. For instance, because purple loosestrife does not tolerate salt water, classifications describing a variety of salt marsh habitats are excluded from these lists. Additionally, many of these classifications are named for predominantly upland habitats that nevertheless contain sometimes-substantial wetland areas where purple loosestrife could potentially occur. Precise distribution information is lacking because of gaps in the understanding of biological and ecological characteristics of non-native species and because introduced species may still be expanding their habitable range. Therefore these lists are speculative and may not be complete.
Regional Distribution in the Western United States
This species can be found in the following regions of the western United States (according to the Bureau of Land Management classification of Physiographic Regions of the western United States):
BLM PHYSIOGRAPHIC REGIONS :
1 Northern Pacific Border
2 Cascade Mountains
3 Southern Pacific Border
4 Sierra Mountains
5 Columbia Plateau
6 Upper Basin and Range
7 Lower Basin and Range
8 Northern Rocky Mountains
9 Middle Rocky Mountains
10 Wyoming Basin
11 Southern Rocky Mountains
12 Colorado Plateau
13 Rocky Mountain Piedmont
14 Great Plains
15 Black Hills Uplift
16 Upper Missouri Basin and Broken Lands
Occurrence in North America
Distribution in the United States
According to the U.S. Fish and Wildlife Service, purple loosestrife now occurs in every state except Florida.
Distribution and Habitat in the United States
More info for the term: rootstock
Purple loosestrife is a non-native, perennial wetland herb [14,129]. Stems are erect, 1 to 8 feet (0.3-2.4 m) tall, becoming woody with age and persisting through winter and up to 2 years [9,14,73,118]. Mature, long-established plants are often 10 feet (3 m) tall and 5 feet (1.5 m) wide . Plants may become increasingly bush-like by producing greater numbers of basal stems from the same rootstock each year [14,79,118,129]. Plants begin producing multiple stems from a single rootstock as early as the 2nd growing season . Anderson  recorded single genets with over 130 stems produced from a single rootstock during a single season. He also estimated ages for individual plants up to 22 years. Observations have been recorded of particular rootstocks failing to generate shoots during a given year, but producing aboveground growth during each prior and subsequent season .
Leaves are 2 to 6 inches (5-14 cm) long and attached close to the stem . Flower spikes vary in length from > 40 inches (1 m) to only a few inches, and only 2 to 3 inches (5.1-7.6 cm) of the spike typically display open flowers at any given time [9,73]. Fruits are capsules 2-3 mm in length . Seeds measure approximately 400 x 200 microns, and weigh approximately 1.8 x 10-6 ounces (50 Âµg) per seed, which is comparatively quite small among North American temperate wetland plants [116,129].
Seedlings quickly develop a thick, hardened taproot . Mature plants subjected to persistent flooding respond by forming aerenchymous (containing large intercellular air spaces) tissue, permitting oxygen flow to submerged roots .
The preceding description provides characteristics of purple loosestrife that may be relevant to fire ecology and is not meant to be used for identification. Keys for identifying purple loosestrife are available in various floras (e.g. [57,71]). Photos and descriptions of purple loosestrife are also available online from Minnesota Sea Grant. Check with the native plant society or cooperative extension service in your area for more information.
Purple loosestrife is an erect perennial herb in the loosestrife family, with a square, woody stem and opposite or whorled leaves. Leaves are lance-shaped, stalkless, and heart-shaped or rounded at the base. Plants are usually covered by a downy pubescence. Loosestrife plants grow from four to ten feet high, depending upon conditions, and produce a showy display of magenta-colored flower spikes throughout much of the summer. Flowers have five to seven petals. Mature plants can have from 30 to 50 stems arising from a single rootstock.
Description and Biology
- Plant: erect perennial herb with a square, woody stem usually covered by downy hair; 4-10 ft. high, depending upon conditions.
- Leaves: lance-shaped, stalk-less and rounded to heart-shaped at the base; arranged in pairs or whorls around the stem.
- Flowers, fruits and seeds: produces a showy display of magenta-colored flower spikes throughout much of the summer. Individual flowers have five to seven petals. A single mature plant can have 30-50 stems arising from one rootstock, and can produce an estimated two to three million seeds per year. The flowering season extends from June to September; flowers require pollination by insects, for which they supply an abundant source of nectar.
- Spreads: through the vast quantity of seeds, dispersed by wind and water. It also readily reproduces vegetatively through underground stems at a rate of about one foot per year.
- Look-alikes: from a distance, purple loosestrife may be confused with blue vervain (Verbena hastata), blazing star (Liatris aspera and L. spicata), Canada germander (Teucrium canadense), swamp milkweed (Asclepias incarnata), and fireweed (Chamaenerion angustifolium), which is native to the northern U.S. and Canada.
At a distance, L. salicaria may be confused with Epilobium angustifolium, Verbena hastata, Teucrium canadense, or Liatris spp. Upon closer examination however, purple loosestrife is easily distinguished from these other magenta-flowered plants.
Habitat and Ecology
L.salicaria will occur in most wetland types from river margins and banks, to low-lying seasonally inundated areas in rough pasture, the margins of wet woodland and even seasonally pools.
More info for the terms: phase, presence
Throughout its global distribution purple loosestrife is strongly linked with temperate climate and moist or saturated soils . Unshaded, newly-exposed, moist soil appears most favorable for seedling establishment. Riverine habitats subjected to periodic but infrequent scouring, or lacustrine habitats subject to periodic water level reduction such as drought-exposed lakeshore or seasonal impoundment drawdown are good examples of habitats at risk of invasion. Once purple loosestrife seedlings become established, adults are quite flood tolerant . Moisture is the most critical factor for growth and reproduction, but well-established plants can persist at dry sites for many years . Keddy and Ellis  examined purple loosestrife seedling recruitment along a water level gradient, simulating conditions ranging from water levels 2 inches (5 cm) below the soil surface to standing water up to 4 inches (10 cm) above the soil surface. They found there was no significant (p = 0.44) effect of water depth on germination and early establishment of seedlings, indicating a broad tolerance for water level in the recruitment phase of purple loosestrife life history. Stream corridors with steep elevational gradients may be less susceptible to colonization by purple loosestrife due to gravitational constraints on seed dispersal .
Northern limits of purple loosestrife distribution may be strongly influenced by low growing season temperature. Under controlled conditions, growth was severely restricted at 46.4 degrees Fahrenheit (8 Â°C) compared with more "characteristic" growth at 64.4 degrees Fahrenheit (18Â°C) .
Purple loosestrife is found on both calcareous and acidic soils [111,113,129] and tolerates low-nutrient soils [111,117,141]. Typically found in open areas, purple loosestrife will tolerate some shade, but growth, reproduction and survival may be substantially reduced under shaded conditions [110,118].
Several characteristics of wetland or riparian habitats have been identified that may be predictive of invasibility by purple loosestrife. Assuming dispersal is largely via floating propagules, isolated wetland basins may be less susceptible to purple loosestrife colonization than areas with interconnected waterways. Additionally, narrow streams with steep gradients are probably less susceptible, because they are frequently scoured and contain fewer areas of slack water, while slower, broader flows are more likely to contain habitat suitable for colonization. Riparian areas that are mostly shaded are also less susceptible because purple loosestrife seedlings require relatively high light levels. Finally, the presence of one or more commonly associated taxa, such as cattails (Typha spp.), reed canarygrass (Phalaris arundinacea), sedges (Carex) spp., and rushes (Juncus spp.) may indicate a habitat that is highly susceptible to invasion by purple loosestrife .
Key Plant Community Associations
habitats in North America, and consequently is associated with a variety of
plant taxa, functional guilds and communities. Habitats where it is likely to be
found include: freshwater marshes [27,93,102,105,127,129], streambanks or lakeshores
seasonally-wet meadows/wet prairies [8,10,129], bogs , vernal ponds , openings in forested swamps
, intermittent streams , shallow impoundments, and ditches and canals
[102,105]. Purple loosestrife is listed by the U.S. Fish and
Wildlife Service Office of Biological Services as a typical broadleaf plant of
Palustrine Persistent Emergent Wetlands .
In a host-specificity test of potential biological
control agents for purple loosestrife, Blossey and Schroeder  included 13
plant species said to "occur in the same habitat" as purple
loosestrife and were "of wildlife importance." Although these species are not necessarily distributed
homogeneously or systematically across the North American
landscape, they likely represent a reasonable sample of typical plant
associates. These species were common cattail (Typha
latifolia), broadfruit bur-reed (Sparganium eurycarpum), broadleaf
arrowhead (Sagittaria latifolia), annual wildrice (Zizania aquatica),
Olney threesquare (Scirpus americanus), hardstem bulrush (Scirpus acutus), longhair sedge (Carex comosa), sandbar willow (Salix
exigua), curly dock (Rumex crispus), longroot smartweed (Polygonum
amphibium), lambsquarters (Chenopodium album), cursed buttercup (Ranunculus
sceleratus) and St. Anthony's turnip (Ranunculus bulbosus).
Classifications describing plant communities in which
purple loosestrife is a dominant species are:
New York 
Habitat: Rangeland Cover Types
This species is known to occur in association with the following Rangeland Cover Types (as classified by the Society for Range Management, SRM):
More info for the terms: cover, fresh, shrub, vine
SRM (RANGELAND) COVER TYPES :
101 Bluebunch wheatgrass
102 Idaho fescue
103 Green fescue
104 Antelope bitterbrush-bluebunch wheatgrass
105 Antelope bitterbrush-Idaho fescue
106 Bluegrass scabland
107 Western juniper/big sagebrush/bluebunch wheatgrass
108 Alpine Idaho fescue
109 Ponderosa pine shrubland
110 Ponderosa pine-grassland
201 Blue oak woodland
202 Coast live oak woodland
203 Riparian woodland
204 North coastal shrub
205 Coastal sage shrub
206 Chamise chaparral
207 Scrub oak mixed chaparral
208 Ceanothus mixed chaparral
209 Montane shrubland
211 Creosote bush scrub
213 Alpine grassland
214 Coastal prairie
215 Valley grassland
216 Montane meadows
301 Bluebunch wheatgrass-blue grama
302 Bluebunch wheatgrass-Sandberg bluegrass
303 Bluebunch wheatgrass-western wheatgrass
304 Idaho fescue-bluebunch wheatgrass
305 Idaho fescue-Richardson needlegrass
306 Idaho fescue-slender wheatgrass
307 Idaho fescue-threadleaf sedge
308 Idaho fescue-tufted hairgrass
309 Idaho fescue-western wheatgrass
310 Needle-and-thread-blue grama
311 Rough fescue-bluebunch wheatgrass
312 Rough fescue-Idaho fescue
313 Tufted hairgrass-sedge
314 Big sagebrush-bluebunch wheatgrass
315 Big sagebrush-Idaho fescue
316 Big sagebrush-rough fescue
317 Bitterbrush-bluebunch wheatgrass
318 Bitterbrush-Idaho fescue
319 Bitterbrush-rough fescue
320 Black sagebrush-bluebunch wheatgrass
321 Black sagebrush-Idaho fescue
322 Curlleaf mountain-mahogany-bluebunch wheatgrass
323 Shrubby cinquefoil-rough fescue
324 Threetip sagebrush-Idaho fescue
401 Basin big sagebrush
402 Mountain big sagebrush
403 Wyoming big sagebrush
404 Threetip sagebrush
405 Black sagebrush
406 Low sagebrush
407 Stiff sagebrush
408 Other sagebrush types
409 Tall forb
410 Alpine rangeland
411 Aspen woodland
412 Juniper-pinyon woodland
413 Gambel oak
414 Salt desert shrub
415 Curlleaf mountain-mahogany
416 True mountain-mahogany
417 Littleleaf mountain-mahogany
418 Bigtooth maple
505 Grama-tobosa shrub
507 Palo verde-cactus
601 Bluestem prairie
602 Bluestem-prairie sandreed
603 Prairie sandreed-needlegrass
604 Bluestem-grama prairie
605 Sandsage prairie
611 Blue grama-buffalo grass
613 Fescue grassland
614 Crested wheatgrass
701 Alkali sacaton-tobosagrass
702 Black grama-alkali sacaton
703 Black grama-sideoats grama
704 Blue grama-western wheatgrass
705 Blue grama-galleta
706 Blue grama-sideoats grama
707 Blue grama-sideoats grama-black grama
710 Bluestem prairie
711 Bluestem-sacahuista prairie
712 Galleta-alkali sacaton
715 Grama-buffalo grass
717 Little bluestem-Indiangrass-Texas wintergrass
719 Mesquite-liveoak-seacoast bluestem
720 Sand bluestem-little bluestem (dunes)
721 Sand bluestem-little bluestem (plains)
722 Sand sagebrush-mixed prairie
723 Sea oats
724 Sideoats grama-New Mexico feathergrass-winterfat
725 Vine mesquite-alkali sacaton
727 Mesquite-buffalo grass
730 Sand shinnery oak
731 Cross timbers-Oklahoma
732 Cross timbers-Texas (little bluestem-post oak)
735 Sideoats grama-sumac-juniper
802 Missouri prairie
803 Missouri glades
804 Tall fescue
807 Gulf Coast fresh marsh
Habitat: Cover Types
This species is known to occur in association with the following cover types (as classified by the Society of American Foresters):
More info for the terms: cover, swamp
SAF COVER TYPES :
1 Jack pine
5 Balsam fir
12 Black spruce
13 Black spruce-tamarack
14 Northern pin oak
15 Red pine
17 Pin cherry
18 Paper birch
19 Gray birch-red maple
20 White pine-northern red oak-red maple
21 Eastern white pine
22 White pine-hemlock
23 Eastern hemlock
24 Hemlock-yellow birch
25 Sugar maple-beech-yellow birch
26 Sugar maple-basswood
27 Sugar maple
28 Black cherry-maple
30 Red spruce-yellow birch
31 Red spruce-sugar maple-beech
32 Red spruce
33 Red spruce-balsam fir
34 Red spruce-Fraser fir
35 Paper birch-red spruce-balsam fir
37 Northern white-cedar
39 Black ash-American elm-red maple
40 Post oak-blackjack oak
42 Bur oak
43 Bear oak
44 Chestnut oak
45 Pitch pine
46 Eastern redcedar
50 Black locust
51 White pine-chestnut oak
52 White oak-black oak-northern red oak
53 White oak
55 Northern red oak
58 Yellow-poplar-eastern hemlock
59 Yellow-poplar-white oak-northern red oak
60 Beech-sugar maple
61 River birch-sycamore
62 Silver maple-American elm
65 Pin oak-sweetgum
66 Ashe juniper-redberry (Pinchot) juniper
67 Mohrs (shin) oak
69 Sand pine
70 Longleaf pine
71 Longleaf pine-scrub oak
72 Southern scrub oak
73 Southern redcedar
74 Cabbage palmetto
75 Shortleaf pine
76 Shortleaf pine-oak
78 Virginia pine-oak
79 Virginia pine
80 Loblolly pine-shortleaf pine
81 Loblolly pine
82 Loblolly pine-hardwood
83 Longleaf pine-slash pine
84 Slash pine
85 Slash pine-hardwood
88 Willow oak-water oak-diamondleaf (laurel) oak
89 Live oak
91 Swamp chestnut oak-cherrybark oak
92 Sweetgum-willow oak
93 Sugarberry-American elm-green ash
94 Sycamore-sweetgum-American elm
95 Black willow
96 Overcup oak-water hickory
97 Atlantic white-cedar
98 Pond pine
103 Water tupelo-swamp tupelo
104 Sweetbay-swamp tupelo-redbay
107 White spruce
108 Red maple
110 Black oak
201 White spruce
202 White spruce-paper birch
203 Balsam poplar
204 Black spruce
205 Mountain hemlock
206 Engelmann spruce-subalpine fir
207 Red fir
208 Whitebark pine
209 Bristlecone pine
210 Interior Douglas-fir
211 White fir
212 Western larch
213 Grand fir
215 Western white pine
216 Blue spruce
218 Lodgepole pine
219 Limber pine
220 Rocky Mountain juniper
221 Red alder
222 Black cottonwood-willow
223 Sitka spruce
224 Western hemlock
225 Western hemlock-Sitka spruce
226 Coastal true fir-hemlock
227 Western redcedar-western hemlock
228 Western redcedar
229 Pacific Douglas-fir
230 Douglas-fir-western hemlock
233 Oregon white oak
234 Douglas-fir-tanoak-Pacific madrone
236 Bur oak
237 Interior ponderosa pine
238 Western juniper
243 Sierra Nevada mixed conifer
244 Pacific ponderosa pine-Douglas-fir
245 Pacific ponderosa pine
246 California black oak
247 Jeffrey pine
248 Knobcone pine
249 Canyon live oak
250 Blue oak-foothills pine
251 White spruce-aspen
252 Paper birch
253 Black spruce-white spruce
254 Black spruce-paper birch
255 California coast live oak
256 California mixed subalpine
Habitat: Plant Associations
This species is known to occur in association with the following plant community types (as classified by Küchler 1964):
More info for the terms: bog, shrub
KUCHLER  PLANT ASSOCIATIONS:
K001 Spruce-cedar-hemlock forest
K002 Cedar-hemlock-Douglas-fir forest
K003 Silver fir-Douglas-fir forest
K004 Fir-hemlock forest
K005 Mixed conifer forest
K006 Redwood forest
K007 Red fir forest
K008 Lodgepole pine-subalpine forest
K009 Pine-cypress forest
K010 Ponderosa shrub forest
K011 Western ponderosa forest
K012 Douglas-fir forest
K013 Cedar-hemlock-pine forest
K014 Grand fir-Douglas-fir forest
K015 Western spruce-fir forest
K016 Eastern ponderosa forest
K017 Black Hills pine forest
K018 Pine-Douglas-fir forest
K020 Spruce-fir-Douglas-fir forest
K021 Southwestern spruce-fir forest
K022 Great Basin pine forest
K023 Juniper-pinyon woodland
K024 Juniper steppe woodland
K025 Alder-ash forest
K026 Oregon oakwoods
K028 Mosaic of K002 and K026
K029 California mixed evergreen forest
K030 California oakwoods
K031 Oak-juniper woodland
K032 Transition between K031 and K037
K034 Montane chaparral
K035 Coastal sagebrush
K036 Mosaic of K030 and K035
K037 Mountain-mahogany-oak scrub
K038 Great Basin sagebrush
K041 Creosote bush
K042 Creosote bush-bur sage
K043 Paloverde-cactus shrub
K045 Ceniza shrub
K046 Desert: vegetation largely lacking
K048 California steppe
K049 Tule marshes
K052 Alpine meadows and barren
K054 Grama-tobosa prairie
K055 Sagebrush steppe
K056 Wheatgrass-needlegrass shrubsteppe
K057 Galleta-threeawn shrubsteppe
K059 Trans-Pecos shrub savanna
K060 Mesquite savanna
K061 Mesquite-acacia savanna
K062 Mesquite-live oak savanna
K063 Foothills prairie
K065 Grama-buffalo grass
K068 Wheatgrass-grama-buffalo grass
K069 Bluestem-grama prairie
K070 Sandsage-bluestem prairie
K072 Sea oats prairie
K073 Northern cordgrass prairie
K074 Bluestem prairie
K075 Nebraska Sandhills prairie
K076 Blackland prairie
K077 Bluestem-sacahuista prairie
K078 Southern cordgrass prairie
K081 Oak savanna
K082 Mosaic of K074 and K100
K083 Cedar glades
K084 Cross Timbers
K085 Mesquite-buffalo grass
K086 Juniper-oak savanna
K087 Mesquite-oak savanna
K088 Fayette prairie
K089 Black Belt
K090 Live oak-sea oats
K093 Great Lakes spruce-fir forest
K094 Conifer bog
K095 Great Lakes pine forest
K096 Northeastern spruce-fir forest
K097 Southeastern spruce-fir forest
K098 Northern floodplain forest
K099 Maple-basswood forest
K100 Oak-hickory forest
K101 Elm-ash forest
K102 Beech-maple forest
K103 Mixed mesophytic forest
K104 Appalachian oak forest
K106 Northern hardwoods
K107 Northern hardwoods-fir forest
K108 Northern hardwoods-spruce forest
K109 Transition between K104 and K106
K110 Northeastern oak-pine forest
K112 Southern mixed forest
K113 Southern floodplain forest
This species is known to occur in the following ecosystem types (as named by the U.S. Forest Service in their Forest and Range Ecosystem [FRES] Type classification):
FRES10 White-red-jack pine
FRES12 Longleaf-slash pine
FRES13 Loblolly-shortleaf pine
FRES21 Ponderosa pine
FRES22 Western white pine
FRES24 Hemlock-Sitka spruce
FRES26 Lodgepole pine
FRES28 Western hardwoods
FRES30 Desert shrub
FRES32 Texas savanna
FRES33 Southwestern shrubsteppe
FRES34 Chaparral-mountain shrub
FRES36 Mountain grasslands
FRES37 Mountain meadows
FRES38 Plains grasslands
FRES40 Desert grasslands
FRES41 Wet Grasslands
FRES42 Annual grasslands
Habitat in the United States
Purple loosestrife is capable of invading many wetland types, including freshwater wet meadows, tidal and non-tidal marshes, river and stream banks, pond edges, reservoirs, and ditches.
Habitat & Distribution
Comments: L. salicaria is native to Eurasia and was first reported from the northeastern coast of North America in 1814, (Stuckey 1980). Although purple loosestrife occurs in nearly all sections of the United States, the heaviest concentrations are in the glaciated wetlands of the northeast. Occurrences west of the Mississippi River appear to be scattered (Stuckey 1980), with the species establishing in reclamation projects in the west (Thompson and Jackson 1982).
Purple loosestrife is found in wetlands such as cattail marshes, sedge meadows, and open bogs. L. salicaria also occurs along stream and river banks and lake shores. In addition, the plant is found in ditches and other disturbed wet soil areas.
L. salicaria grows best in high organic soils, but tolerates a wide range of soils including clay, sand, muck, and silt (Thompson and Jackson 1982). Generally, the plant is found in full sun, but it can survive in 50% shade (Thompson and Jackson 1982). Typical associates include Typha latifolia, T. glauca, Phragmites australis, Spartina sp., Scirpus spp., and Carex spp. (Thompson and Jackson 1982).
Flower-Visiting Insects of Purple Loosestrife in Illinois
(insect activity is largely unspecified; information is limited to bees and beetles; observations are from Grundel et al. and Williams)
Apidae (Apinae): Apis mellifera (Gnd); Apidae (Bombini): Bombus impatiens (Gnd); Megachilidae (Coelioxini): Coelioxys modesta sn (Gnd)
Halictidae (Halictinae): Agapostemon sericeus (Gnd), Augochlora pura (Gnd), Halictus confusus (Gnd)
Cantharidae: Chauliognathus pennsylvanicus (Wms)
sn = sucks nectar
Flower-Visiting Insects of Purple Loosestrife in Illinois
(insect activity is largely unspecified; information is limited to bees; observations are from Grundel et al.)
Apidae (Apinae): Apis mellifera (Gnd); Apidae (Bombini): Bombus impatiens (Gnd); Megachilidae (Coelioxini): Coelioxys modesta sn (Gnd)
Halictidae (Halictinae): Agapostemon sericeus (Gnd), Augochlora pura (Gnd), Halictus confusus (Gnd)
imago of Altica lythri grazes on leaf of Lythrum salicaria
Foodplant / open feeder
imago of Altica palustris grazes on leaf of Lythrum salicaria
Foodplant / open feeder
larva of Ametastegia equiseti grazes on leaf of Lythrum salicaria
Other: major host/prey
Foodplant / open feeder
imago of Aphthona lutescens grazes on leaf of Lythrum salicaria
Other: sole host/prey
In Great Britain and/or Ireland:
Foodplant / saprobe
effuse colony of Coremiella dematiaceous anamorph of Coremiella cubispora is saprobic on dead stem of Lythrum salicaria
Remarks: season: 7-10
Other: major host/prey
Foodplant / parasite
Erysiphe lythri parasitises Lythrum salicaria
Foodplant / open feeder
imago of Galerucella calmariensis grazes on leaf of Lythrum salicaria
Foodplant / open feeder
imago of Galerucella pusilla grazes on leaf of Lythrum salicaria
Foodplant / internal feeder
larva of Hylobius transversovittatus feeds within rootstock (woody) of Lythrum salicaria
Other: sole host/prey
Foodplant / saprobe
apothecium of Lachnum salicariae is saprobic on dead stem (base) of Lythrum salicaria
Foodplant / open feeder
imago of Lythraria salicariae grazes on leaf of Lythrum salicaria
Foodplant / internal feeder
larva of Nanophyes marmoratus feeds within ovules of Lythrum salicaria
Other: sole host/prey
Foodplant / feeds on
larva of Phytobius comari feeds on Lythrum salicaria
Foodplant / open feeder
imago of Psylliodes picina grazes on leaf of Lythrum salicaria
Foodplant / spot causer
epiphyllous, punctiform pycnidium of Septoria coelomycetous anamorph of Septoria brissaceana causes spots on live leaf of Lythrum salicaria
Remarks: season: 7-9
Foodplant / saprobe
fruitbody of Sistotrema octosporum is saprobic on dead, decayed stem of Lythrum salicaria
Other: minor host/prey
Foodplant / parasite
hypophyllous colony of Stenella dematiaceous anamorph of Stenella lythri parasitises dying leaf of Lythrum salicaria
Purple loosestrife begins to bloom in July and continues until September or October. The flowers are pollinated by several different types of bees from the Megachilinae, Apinae, Xylopinae, and Bombinae; and by several butterflies: Pieris rapae, Colias philodice, and Cercyonis pegala (Balogh 1985). Seed production is prolific. There is an average of 120 seeds per capsule and up to 900 capsules per plant (Rawinski 1982). The lowest capsules on the stem are dehiscing while the upper stem capsules are still green.
The seeds are small, weighing 0.06 mg each (Shamsi and Whitehead 1974). Dispersal is mainly by wind, but seeds can also be transported on the feet of waterfowl or other wetland animals. Red-winged blackbirds have been observed eating the seeds (Rawinski 1982). Humans carry seeds inadvertently on clothing and shoes and in some instances, bee-keepers have purposely sown seeds in headwaters and wetlands to provide a steady source of nectar for their bees. The seeds and cotyledon stage seedlings are buoyant and can be dispersed by water currents (Balogh 1985). The seed bank potential for L. salicaria is enhanced by the high viability of the seeds. Viability decreased from 99% to 80% after two years of storage in a natural body of water (Rawinski 1982).
Seeds of L. salicaria can germinate in acidic or alkaline soils; in soils that are nutrient rich or nutrient poor. Light requirements for germination are minimal (Shamsi and Whitehead 1974). Temperature at the soil surface is a critical factor for germination. Seeds will germinate at temperatures ranging from 15 to 20 degrees C (Balogh 1985). Seeds germinate in high densities--about 10,000 to 20,000/sq. meter (Rawinski 1982). The interval between germination and flowering is eight to ten weeks (Rawinski 1982).
Seedlings that germinate in the spring grow rapidly and will produce a floral shoot up to 30 cm in length the first year. Summer-germinated seedlings develop only five or six pairs of leaves before the end of the growing season (Shamsi and Whitehead 1974). Spring-germinated seedlings have a higher survival rate than summer-germinated seedlings. Open grown shoots have a greater reproductive output than shoots growing in dense stands (Rawinski 1982). Once established, seedlings can survive shallow flooding of up to 30-45 cm in depth (Thompson and Stuckey 1980.).
The taproot is strongly developed in the seedling stage and persists throughout the life of the plant (Shamsi and Whitehead 1974). In mature plants, the taproot and major root branches become thick and woody (Rawinski 1982). The semi-woody aerial shoots die in the fall but persist for one to two years making stands of L. salicaria very dense. New shoots arise the following spring from buds at the top of the rootstocks (Rawinski 1982).
The rootstock is the main organ of perennation and vegetative spread is therefore limited (Shamsi and Whitehead 1974). L. salicaria can spread vegetatively by resprouting from cut stems and regenerating from pieces of root stock (Rawinski 1982).
Infestations of purple loosestrife appear to follow a pattern of establishment, maintenance at low numbers, and then dramatic population increases when conditions are optimal. L. salicaria flourishes in wetland habitats that have been disturbed or degraded from draining, natural drawdown in dry years, bulldozing, siltation, shore manipulation, cattle trampling, or dredging. Mudflats exposed following drawdowns will be quickly colonized if a loosestrife seed source is present. Seeds are usually present in such large numbers and germinate in such high densities that growth of native seedlings is suppressed (Rawinski 1982). Loosestrife crowds or shades out native species and eventually becomes a virtually monospecific stand.
L. salicaria is an extremely successful invader of wetlands that have been subjected to some type of disturbance: drawdown, siltation, drainage, ditching. Expansion in a wetland can be extensive and sudden due to the abundance of seeds produced and the rapid growth of seedlings. High seed viability and prolific seed production can build up a seed bank of massive proportions.
Purple loosestrife seed germinates in such high densities that it outcompetes native seedlings. The buildup of debris around the roots enable loosestrife to invade deeper water and to form dense stands that shade out other emergents and push out floating vegetation by closing open water spaces.
Plant Response to Fire
Although no direct evidence exists, it is likely that purple loosestrife will survive fire by sprouting from buds located below the soil surface on the root crown [46,111].
Broad-scale Impacts of Fire
Reports of interactions between purple loosestrife and fire usually attest to the difficulty associated with trying to burn plants as a control method. Such attempts are commonly described as being confounded by moist soil conditions and patchy fuel distribution [80,83,102,129]. Because postsenescent purple loosestrife retains persistent standing dead stem material , it is possible that dry winter or early spring conditions may permit dense stands to carry fire, but this is speculative.
Immediate Effect of Fire
Information describing the effect of fire on purple loosestrife is sparse, but several authors suggest that it does not burn well [83,129]. In a review, Haber  suggest that "fires generally do not burn at high enough temperatures to kill the root crown, especially in damp soils." Rawinski  indicated that individual plants will burn, but conditions that permit a fire to carry through purple loosestrife stands are probably not common.
Fire adaptations: Purple loosestrife is an herbaceous perennial, with growing points that overwinter on the root crown about 0.8 inches (2 cm) below the soil surface (see Botanical and Ecological Characteristics) . FIRE REGIMES: Because purple loosestrife is distributed across many habitats in North America (see Distribution and Occurrence), FIRE REGIMES associated with the species vary. Recurrence and behavior of fire in areas where purple loosestrife occurs is likely to be closely tied to particular local FIRE REGIMES, and cannot be easily summarized over broad spatial scales. Given purple loosestrife's moisture requirements, it is unlikely to occur in areas experiencing frequently recurring fire. Similar to many areas that experience fire infrequently, occurrence of fire in areas where purple loosestrife is found is likely to driven by drought. However, information describing interactions between purple loosestrife and fire are lacking, and information linking purple loosestrife to specific North American FIRE REGIMES is nonexistent.
Given the dearth of information on fire and purple loosestrife and our relatively poor understanding of how purple loosestrife generally affects plant community dynamics where it occurs, any description of interactions between particular FIRE REGIMES and purple loosestrife is speculative. Where purple loosestrife displaces native vegetation dependent upon recurring fire for maintenance of a seral stage, persistent stands of invasive purple loosestrife may alter FIRE REGIMES if purple loosestrife burns less frequently or less readily than the native vegetation it displaces. For example, sedge meadow communities along the St. Lawrence River in southern Quebec where purple loosestrife is sometimes found, are historically maintained by dormant season fire recurring every 1 to 3 years. If invading purple loosestrife reduces fire frequency or severity at these sites, these communities are likely to succeed to woody species such as willow (Salix spp.) or maple (Acer spp.) .
The following table lists fire return intervals for communities or ecosystems throughout North America where purple loosestrife may occur. This list is not intended as a description of purple loosestrife distribution, but rather as a guide to FIRE REGIMES in areas where purple loosestrife could potentially be found. (For more specific distributional information see Distribution and Occurrence). While this list mainly describes upland habitats, purple loosestrife is generally associated with wetland or riparian habitats within these communities or ecosystems. As such, this list is meant as a guideline to illustrate historic FIRE REGIMES and is not to be interpreted as a strict description of FIRE REGIMES for purple loosestrife.
|Community or Ecosystem||Dominant Species||Fire Return Interval Range (years)|
|silver fir-Douglas-fir||Abies amabilis-Pseudotsuga menziesii var. menziesii||> 200|
|grand fir||Abies grandis||35-200 |
|silver maple-American elm||Acer saccharinum-Ulmus americana|
|sugar maple||Acer saccharum||> 1000|
|sugar maple-basswood||Acer saccharum-Tilia americana||> 1000 |
|California chaparral||Adenostoma and/or Arctostaphylos spp.||95]|
|bluestem prairie||Andropogon gerardii var. gerardii-Schizachyrium scoparium||69,95]|
|Nebraska sandhills prairie||Andropogon gerardii var. paucipilus-Schizachyrium scoparium|
|bluestem-Sacahuista prairie||Andropogon littoralis-Spartina spartinae|
|sagebrush steppe||Artemisia tridentata/Pseudoroegneria spicata||20-70|
|basin big sagebrush||Artemisia tridentata var. tridentata||12-43 |
|mountain big sagebrush||Artemisia tridentata var. vaseyana||15-40 [6,25,85]|
|Wyoming big sagebrush||Artemisia tridentata var. wyomingensis||10-70 (40**) [133,143]|
|coastal sagebrush||Artemisia californica|
|saltbush-greasewood||Atriplex confertifolia-Sarcobatus vermiculatus|
|desert grasslands||Bouteloua eriopoda and/or Pleuraphis mutica||5-100|
|plains grasslands||Bouteloua spp.|
|blue grama-needle-and-thread grass-western wheatgrass||Bouteloua gracilis-Hesperostipa comata-Pascopyrum smithii|
|blue grama-buffalo grass||Bouteloua gracilis-Buchloe dactyloides|
|California montane chaparral||Ceanothus and/or Arctostaphylos spp.||50-100 |
|sugarberry-America elm-green ash||Celtis laevigata-Ulmus americana-Fraxinus pennsylvanica||135]|
|paloverde-cactus shrub||Cercidium microphyllum/Opuntia spp.||95]|
|curlleaf mountain-mahogany*||Cercocarpus ledifolius||13-1000 [7,109]|
|mountain-mahogany-Gambel oak scrub||Cercocarpus ledifolius-Quercus gambelii||95]|
|Atlantic white-cedar||Chamaecyparis thyoides||35 to > 200 |
|northern cordgrass prairie||Distichlis spicata-Spartina spp.||1-3 |
|beech-sugar maple||Fagus spp.-Acer saccharum||> 1000 |
|California steppe||Festuca-Danthonia spp.||95]|
|black ash||Fraxinus nigra||135]|
|juniper-oak savanna||Juniperus ashei-Quercus virginiana|
|Ashe juniper||Juniperus ashei|
|western juniper||Juniperus occidentalis||20-70|
|Rocky Mountain juniper||Juniperus scopulorum|
|cedar glades||Juniperus virginiana||3-7|
|tamarack||Larix laricina||35-200 |
|western larch||Larix occidentalis||25-100 |
|Ceniza shrub||Larrea tridentata-Leucophyllum frutescens-Prosopis glandulosa||95]|
|wheatgrass plains grasslands||Pascopyrum smithii||95]|
|Great Lakes spruce-fir||Picea-Abies spp.||35 to > 200|
|northeastern spruce-fir||Picea-Abies spp.||35-200 |
|southeastern spruce-fir||Picea-Abies spp.||35 to > 200 |
|Engelmann spruce-subalpine fir||Picea engelmannii-Abies lasiocarpa||35 to > 200 |
|black spruce||Picea mariana||35-200|
|conifer bog*||Picea mariana-Larix laricina||35-200 |
|blue spruce*||Picea pungens||35-200 |
|red spruce*||P. rubens||35-200 |
|pine-cypress forest||Pinus-Cupressus spp.||5]|
|whitebark pine*||Pinus albicaulis||50-200 |
|jack pine||Pinus banksiana||33]|
|Mexican pinyon||Pinus cembroides||20-70 [86,126]|
|Rocky Mountain lodgepole pine*||Pinus contorta var. latifolia||25-300+ [4,5,107]|
|Sierra lodgepole pine*||Pinus contorta var. murrayana||35-200 |
|shortleaf pine||Pinus echinata||2-15|
|shortleaf pine-oak||Pinus echinata-Quercus spp.||135]|
|Colorado pinyon||Pinus edulis||10-49 |
|slash pine||Pinus elliottii||3-8|
|slash pine-hardwood||Pinus elliottii-variable|
|sand pine||Pinus elliottii var. elliottii||25-45 |
|South Florida slash pine||Pinus elliottii var. densa||1-5 [88,135]|
|Jeffrey pine||Pinus jeffreyi||5-30|
|western white pine*||Pinus monticola||50-200|
|Pacific ponderosa pine*||Pinus ponderosa var. ponderosa||1-47|
|interior ponderosa pine*||Pinus ponderosa var. scopulorum||2-10 |
|Table Mountain pine||Pinus pungens||135]|
|red pine (Great Lakes region)||Pinus resinosa||10-200 (10**) [33,37]|
|red-white-jack pine*||Pinus resinosa-P. strobus-P. banksiana||10-300 [33,54]|
|pitch pine||Pinus rigida||6-25 [24,55]|
|pond pine||Pinus serotina||3-8|
|eastern white pine||Pinus strobus||35-200|
|eastern white pine-eastern hemlock||Pinus strobus-Tsuga canadensis||35-200|
|eastern white pine-northern red oak-red maple||Pinus strobus-Quercus rubra-Acer rubrum||35-200|
|loblolly pine||Pinus taeda||3-8|
|loblolly-shortleaf pine||Pinus taeda-P. echinata||10 to|
|Virginia pine||Pinus virginiana||10 to|
|Virginia pine-oak||Pinus virginiana-Quercus spp.||10 to|
|sycamore-sweetgum-American elm||Platanus occidentalis-Liquidambar styraciflua-Ulmus americana||135]|
|galleta-threeawn shrubsteppe||Pleuraphis jamesii-Aristida purpurea|
|eastern cottonwood||Populus deltoides||95]|
|aspen-birch||Populus tremuloides-Betula papyrifera||35-200 [33,135]|
|quaking aspen (west of the Great Plains)||Populus tremuloides||7-120 [5,45,84]|
|mesquite-buffalo grass||Prosopis glandulosa-Buchloe dactyloides|
|Texas savanna||Prosopis glandulosa var. glandulosa||95]|
|black cherry-sugar maple||Prunus serotina-Acer saccharum||> 1000 |
|mountain grasslands||Pseudoroegneria spicata||3-40 (10**) [4,5]|
|Rocky Mountain Douglas-fir*||Pseudotsuga menziesii var. glauca||25-100 |
|coastal Douglas-fir*||Pseudotsuga menziesii var. menziesii||40-240 [5,87,106]|
|California mixed evergreen||Pseudotsuga menziesii var. m.-Lithocarpus densiflorus-Arbutus menziesii|
|California oakwoods||Quercus spp.||5]|
|oak-juniper woodland (Southwest)||Quercus-Juniperus spp.||95]|
|northeastern oak-pine||Quercus-Pinus spp.||10 to 135]|
|oak-gum-cypress||Quercus-Nyssa-spp.-Taxodium distichum||35 to > 200 |
|southeastern oak-pine||Quercus-Pinus spp.||135]|
|coast live oak||Quercus agrifolia||5]|
|white oak-black oak-northern red oak||Quercus alba-Q. velutina-Q. rubra||135]|
|canyon live oak||Quercus chrysolepis|
|blue oak-foothills pine||Quercus douglasii-Pinus sabiana||5]|
|northern pin oak||Quercus ellipsoidalis||135]|
|Oregon white oak||Quercus garryana||5]|
|bear oak||Quercus ilicifolia||135]|
|California black oak||Quercus kelloggii||5-30 |
|bur oak||Quercus macrocarpa||135]|
|oak savanna||Quercus macrocarpa/Andropogon gerardii-Schizachyrium scoparium||2-14 [95,135]|
|chestnut oak||Q. prinus||3-8|
|northern red oak||Quercus rubra||10 to|
|post oak-blackjack oak||Quercus stellata-Q. marilandica|
|black oak||Quercus velutina|
|live oak||Quercus virginiana||10 to135]|
|interior live oak||Quercus wislizenii||5]|
|cabbage palmetto-slash pine||Sabal palmetto-Pinus elliottii||88,135]|
|blackland prairie||Schizachyrium scoparium-Nassella leucotricha|
|Fayette prairie||Schizachyrium scoparium-Buchloe dactyloides|
|little bluestem-grama prairie||Schizachyrium scoparium-Bouteloua spp.|
|tule marshes||Scirpus and/or Typha spp.||95]|
|redwood||Sequoia sempervirens||5-200 [5,36,124]|
|southern cordgrass prairie||Spartina alterniflora||1-3 |
|baldcypress||Taxodium distichum var. distichum||100 to > 300|
|pondcypress||Taxodium distichum var. nutans||88]|
|western redcedar-western hemlock||Thuja plicata-Tsuga heterophylla||> 200 |
|eastern hemlock-yellow birch||Tsuga canadensis-Betula alleghaniensis||> 200 |
|western hemlock-Sitka spruce||Tsuga heterophylla-Picea sitchensis||> 200|
|mountain hemlock*||Tsuga mertensiana||35 to > 200 |
More info on this topic.
More info for the terms: cohort, genet, marsh, natural, succession
The ways and extent to which purple loosestrife affects succession in wetland plant communities are not altogether clear. It is evident that purple loosestrife requires open, moist, bare substrate for establishment (see Site Characteristics and Regeneration Processes). It is generally agreed that purple loosestrife is a pioneer or gap-colonizing species that quickly responds to site disturbance by recruiting often-substantial numbers of new genets from a pre-existing seed bank [1,30,110].
Purple loosestrife displays many characteristics typical of pioneer species, such as rapid maturity, high seed production, tolerance of nutrient-poor environments, and high germination success. Yet North American populations, once established, also are potentially long-lived (22+ years), capable of growing to a relatively large size, and have shown the propensity for near-continuous, low-level recruitment in the absence of large-scale disturbance [1,129]. While evidence is somewhat limited, it is speculated natural mortality rates in adult plants are quite low .
Purple loosestrife, once established, can persist within a site for relatively long periods, even in the absence of frequent disturbance. After examining purple loosestrife population structure within several different communities in eastern Massachusetts, Anderson  concluded low levels of nearly-continuous recruitment are likely to occur in areas where mature plants (and the inevitable prodigious purple loosestrife seed bank) are present. Additionally, this trend is punctuated by occasional disturbances that provide conditions suitable for short-lived recruitment episodes in which relatively large cohorts of new plants are established.
But there is some question regarding the view that purple loosestrife inevitably dominates invaded sites in virtual monotypic stands. Anderson  points out that in a widely cited review by Thompson and others , estimates of the proportion of stand biomass attributed to purple loosestrife, which ostensibly increased over time following establishment, may instead have been attributable to increases in the number of stems per genet rather than greater numbers of individual plants. The number of annually produced stems per single genetically distinct plant has been shown to be a good predictor of the age of that individual . Anderson  also notes observations described in Thompson and others  were strictly visual assessments, and since no hard data was collected, there is no way to definitively ascertain what, if any, changes in biomass distribution among species may have occurred.
In its native range, European populations of purple loosestrife may also form large monospecific stands following pregrowing season disturbance, but are prone to invasion by other species soon after stand establishment [110,111]. Whitehead  described the gradual yielding of monospecific stands of purple loosestrife to mixed species communities in England as being due to slow growth of purple loosestrife during periods of cool spring temperatures compared with competitors possessing low-temperature growth capabilities such as cattails or reeds (Phragmites spp.) It is likely that an aggregate of factors act to limit purple loosestrife site dominance in its native habitats .
Thompson and others  have reviewed several historical accounts of purple loosestrife stands, both in its native Europe and elsewhere. They determined that while purple loosestrife seldom maintains strong community dominance in native (European) habitats, it commonly forms dense, long-lasting, virtually monospecific stands in areas where it is not native, especially temperate North America. They considered 3 factors that could possibly account for this phenomenon: 1) the absence of many key insect predators that effectively reduce competitiveness of European purple loosestrife plants, 2) predominance of the muskrat in its native North American habitat and the impact of its selective Foraging behavior on cattails (see Importance to Livestock and Wildlife or Impacts and Control), and 3) the possibility that North American purple loosestrife may have evolved adaptive traits which make it more vigorous and competitive than its European relatives.
Many factors are likely to affect the ability of purple loosestrife to form and maintain extensive monodominant stands in North American wetlands. Characteristics particular to certain classes of habitat may lead to monodominance. Auclair and others  have noted some trends in 2 distinct plant communities of Huntington Marsh, located along the St. Lawrence River near the junction of the Quebec, Ontario and New York borders. In the emergent aquatic community, the dominant emergent taxa tended to exclude each other, resulting in a mosaic of nearly monospecific communities. In particular, river bulrush (Schoenoplectus fluviatilis), common reed (Phragmites australis) and narrow-leaved cattail (Typha angustifolia) displayed this phenomenon. In contrast, sedge meadow communities were much more diverse and lacked the dominance and segregation of species. Instead they demonstrated subtle gradients in composition that were generally difficult to discern.
The nature of particular disturbance events may also impact initial floristics and subsequent successional trajectories. For instance, the relative competitiveness of purple loosestrife seedlings following disturbance may depend upon when initiation of the new seedling community occurs within the growing season. Because purple loosestrife growth rates are closely linked to day length , early summer establishment of a seedling cohort or community, compared with late summer establishment, is more likely to result in a monospecific stand of purple loosestrife because purple loosestrife seedlings will be more competitive .
More research is needed to help elucidate the means and extent to which purple loosestrife alters successional trajectories and community dynamics. Long-term studies that examine preinvasion vs. postinvasion data would be particularly helpful.
Breeding system: Purple loosestrife is a tristylous species (3 different style lengths), usually in a 1:1:1 ratio, indicating sexual reproduction is probably its most important means of regeneration . It is primarily an outcrosser, as self-pollination in purple loosestrife is rare, and has been shown to reduce seed production .
Pollination: Purple loosestrife is insect pollinated. Most reports indicate honeybees are the main pollinators [43,73]. Others include bumblebees [72,73], leaf-cutter bees and carpenter bees , as well as a variety of butterflies [72,73]. Hummingbirds have been observed taking nectar from purple loosestrife in British Columbia , although pollination by hummingbirds is undocumented.
Seed production: Purple loosestrife produces an immense number of seeds. Estimates of seed production rates range from just over 100,000 seeds per plant for young plants with single stems , to over 2.5 million seeds per plant for established plants with an average of 30 stems per plant . Although perennial, purple loosestrife is capable of producing viable seed during its 1st growing season . Seed output is largely a function of plant age, size, and vigor . Shoots growing in relatively dense stands tend to produce fewer and smaller inflorescences than those growing in more open areas .
Seed dispersal: Because seeds are small and light they are thought to be dispersed, at least in part, by wind [53,111]. However, Thompson and others  report observations that seedling densities decline sharply within a 33 foot (10 m) perimeter of the parent plant and seedlings are often distributed downslope from the parent plant rather than downwind, suggesting a limited role for wind dispersal. Dispersal via moving water is also likely [53,118,119]. Seeds and cotyledon stage seedlings are reportedly buoyant , although there are reports that purple loosestrife seeds don't float . Floating seeds may disperse to suitable sites for establishment. Seeds that sink may germinate while submerged, then rise to the surface and drift to suitable sites for establishment . Seeds may be transported in fur of mammals, plumage of waterfowl, mud attached to footgear, vehicle treads or cooling systems of outboard motors [53,128,129]. Thompson and others  also suggest birds may deposit ingested seeds in areas where wind or gravity-mediated dispersal seems unlikely.
Seed banking: Given its high seed output and ability to produce seed in its 1st growing season, purple loosestrife can establish substantial soil seed banks. Seeds may remain viable for at least 2 to 3 years [102,111], although the long-term viability of seeds stored in the soil seed bank remains under investigation . Seeds may remain viable even when subjected to saturating conditions. Viability of seeds that were stored underwater was tested at 4-month intervals under ideal germination conditions. Germination declined from an initial rate of 99% to 93% after 1 year and 80% after 2 years .
Purple loosestrife has the potential to dominate the soil seed bank where it becomes well established. Soil samples taken from within purple loosestrife stands in emergent wetlands in southeastern Minnesota contained an average of 37,963 purple loosestrife seeds per ft2 (410,000 /m2) in the top 2 in (5 cm) of soil. Seeds were distributed within this entire profile and seed density increased with proximity to the soil surface. Under greenhouse conditions chosen to promote germination, and using soil samples from the above source spread 0.4 in (1 cm) deep, recruitment failed to exhaust the seed bank [138,140]. From the same experiment, purple loosestrife seedlings were found in 91% of untreated (no herbicide) 6.6 x 6.6 feet (2 x 2 m) quadrats, the most frequently encountered species in the soil seed bank .
Germination: Germination is greatest in unshaded, wet soils, with temperatures >68 degrees Fahrenheit (20Âº C) . Shamsi and Whitehead  demonstrated germination is constrained at low temperatures between about 50 to 59 degrees Fahrenheit (10Â°-15Â° C), and no germination occurred below 57 degrees Fahrenheit (14Â° C). Experimental evidence indicates seed dormancy may be enforced by burial, with germination response decreasing linearly (p = 0.001, r2 = 0.89) from 90% at the soil surface to 0% at 0.8 in (2 cm), even under conditions known to promote germination in wetland plants . Any disturbance that redistributes seeds to within the upper 0.8 inch (2 cm) of soil is likely to promote germination. Although light exposure is a prerequisite for germination, length of exposure does not appear important . Purple loosestrife seeds are capable of germinating underwater .
Seedling establishment/growth: Favorable recruitment conditions are largely a function of disturbance that creates areas where little to no vegetation is present . Estimates of maximum initial seedling density vary greatly, from 926 to 1,852 foot-2 (10,000-20,000 m-2) on bare open mudflats  to 2.8 to 4.6 foot-2 (30-50 m-2) in vegetated semiflooded wetlands. In areas where large numbers of seeds are present in the seed bank, small changes in area favorable for establishment can yield large fluctuations in recruitment .
Growth is limited by cold temperature and is considerably slowed at around 46 to 50 degrees Fahrenheit (8-10Âº C) . Light availability can also limit growth and development. Under diminishing light intensities, vegetative growth is slowed, the numbers of flowers, fruits, and seeds per fruit are fewer, and the average dry weight of fruits declines, but there is no change in average dry weight of individual seeds . Growth is also affected by day length. Shamsi and Whitehead  found leaf area and plant dry weight were significantly (P<0.05) reduced when plants were subjected to a 9-hour photoperiod compared with a 16-hour photoperiod. Plants in the 9-hour treatment grew in a comparatively flattened, semi-prostrate condition.
Asexual regeneration: The rootstock is the main organ of perennation, and unaided wide vegetative spread is unlikely. New shoots arise from buds at the top of the rootstock . Root crowns expand annually to accommodate increasing numbers of shoots, but may reach maximum growth at around 20 inches (0.5 m) in diameter .
Purple loosestrife can consistently resprout in response to aboveground damage, often fairly rapidly. A greenhouse experiment showed 91% of clipped seedlings resprouted within 42 days . Live stems that are dislodged and buried can give rise to new shoots via adventitious buds [23,129].
Growth Form (according to Raunkiær Life-form classification)
More info for the terms: helophyte, hemicryptophyte
RAUNKIAER  LIFE FORM:
Life History and Behavior
Biology and Spread
Purple loosestrife enjoys an extended flowering season, generally from June to September, which allows it to produce vast quantities of seed. The flowers require pollination by insects, for which it supplies an abundant source of nectar. A mature plant may have as many as thirty flowering stems capable of producing an estimated two to three million, minute seeds per year.
Purple loosestrife also readily reproduces vegetatively through underground stems at a rate of about one foot per year. Many new stems may emerge vegetatively from a single rootstock of the previous year. "Guaranteed sterile" cultivars of purple loosestrife are actually highly fertile and able to cross freely with purple loosestrife and with other native Lythrum species. Therefore, outside of its native range, purple loosestrife of any form should be avoided.
Molecular Biology and Genetics
Barcode data: Lythrum salicaria
Statistics of barcoding coverage: Lythrum salicaria
Public Records: 4
Specimens with Barcodes: 16
Species With Barcodes: 1
IUCN Red List Assessment
Red List Category
Red List Criteria
National NatureServe Conservation Status
Rounded National Status Rank: NNA - Not Applicable
Rounded National Status Rank: NNA - Not Applicable
NatureServe Conservation Status
Rounded Global Status Rank: G5 - Secure
Please consult the PLANTS Web site and your State Department of Natural Resources for this plant’s current status, such as, state noxious status, and wetland indicator values.
L.salicaria is widespread and abundant throughout its native range and is extremely abundant in parts of its introduced range.
There are no conservation measures in place or needed.
Management Requirements: Once purple loosestrife becomes established in a wetland it displaces endemic vegetation through rapid growth and heavy seed production (Rawinski 1982). L. salicaria has a detrimental impact on native wetland vegetation and associated wildlife. Important wildlife food plants such as cattails and pondweed are displaced or shaded out as L. salicaria expands across a wetland. If purple loosestrife is left unchecked, the wetland eventually becomes a monoculture of loosestrife (Rawinski 1982). The invasion of L. salicaria leads to a loss of plant diversity, which also leads to a loss of wildlife diversity.
Management objectives may include eradicating populations, containing populations or preventing establishment. Monitoring should be used to track the accomplishment of these objectives.
The best time to search for purple loosestrife is in July and August when the plants are blooming. The bright magenta flowers are easy to spot at a great distance. Aerial surveys can be used to note the yearly position of large populations. An advancing or receding boundary would be identifiable from air photos. Ground surveys are more feasible for tracking small populations and finding newly established populations. Look for seedlings in June.
The following individuals are involved in public awareness campaigns or wetland surveys:
John Schwegman, Director, Botany Program, Illinois Dept. Conservation, Springfield, Illinois 62706.
Rich Henderson, Consultant, Natural Areas Management, 2845 Timberlane Verona, Wisconsin 53593.
Noel Cutright, Purple Loosestrife Task Force, 3352 Knollwood Rd., West Bend, Wisconsin 53095.
Purple loosestrife Survey-Nevin, Wisconsin Dept. Natural Resources, P.O. Box 7921, Madison, Wisconsin 53791.
Jay Rendall, Coordinator, Purple Loosestrife Program, Minnesota Dept. Natural Resources, Box 25, 500 Lafayette Rd., St. Paul, MN 55155.
Several control methods have been attempted with varying degrees of success. Natural area managers must determine their objectives first. Is it more feasible to contain or control populations of purple loosestrife? Large populations extending over three acres or more will be difficult if not impossible to completely eradicate using presently known methods. These large populations should be contained at their present position. Preventing the expansion can be accomplished through hand-pulling new plants along the periphery or spraying herbicide on plants extending beyond the main body of the population. Smaller populations can be controlled through eradication. Populations up to three acres can be cleared with herbicides or hand-pulled, depending upon the size of the work crew and time available.
CHEMICAL: The herbicide glyphosate is most commonly used to control L. salicaria. Glyphosate is available under the trade names RoundupTM and RodeoTM, manufactured by Monsanto. Roundup cannot be used over water. Another formulation of glyphosate known as Rodeo contains a non-ionic surfactant and has been approved for use over water. Ortho X-77 is the non-ionic surfactant recommended for use with Rodeo, but several other non-ionic surfactants were cleared for use with Rodeo in 1985 (Balogh 1985).
The major disadvantage in using Rodeo is that glyphosate is a non-specific systemic. Broadcast spraying of non-selective herbicides kills all of the vegetation and may result in an increase in loosestrife density because of seed germination following the removal of competing perennial vegetation (Minnesota DNR 1987). Spot application of Rodeo directly onto L. salicaria would ensure that no large holes would appear in the marsh vegetation and that competition would be unaffected. The safest method of applying glyphosate herbicide is to cut off all stems at about 6 inches and then paint or drip onto the cut surface a 20-30% solution (Henderson 1987).
Spraying should be done after the period of peak bloom, usually late August (Balogh 1985, Rawinski 1982). One to two percent solutions of Rodeo have been recommended as sufficient to kill L. salicaria (Henderson 1987, Minnesota DNR 1987, Balogh 1985, Thrune pers. comm.). Work done by Jim Reinartz at the U.W.-Milwaukee Field Station indicates it is best to spray no more than 25-50% of a plant's foliage (Henderson 1987). This will help protect against overspraying which might damage adjacent vegetation.
It is critical that any control effort be followed up the same growing season and for several years afterwards since some plants will be missed, new seedlings may sprout from the extensive seed bank, and a few plants will survive the low-dosage treatment (Henderson 1987, Minnesota DNR 1987). Higher dosage and careless application, however, inevitably kills more surrounding vegetation and leads to establishment of loosestrife seedlings (Minnesota DNR 1987).
For larger infestations where spot application of glyphosate is not practical, broadleaf herbicides can be used. They have the advantage of not harming monocot species, which are the dominants in most wetland types. Broadleaf herbicides (2,4-D based) can be effective on loosestrife if applied in late May or early June (Henderson 1987). The disadvantage of treating early in the season is that purple loosestrife plants are easily overlooked when not in flower. A combination of 2,4-D and dicamba has been used on a limited basis in western irrigation ditches (Jackson pers. comm.). The EPA has approved a 1:1 tank mix of these two products. Once L. salicaria has reached 10-15% of its mature growth, it can be sprayed with good results. To ensure complete coverage and compensate for spotty application, repeat the treatment once during the growing season (Jackson pers. comm.).
PULLING: Hand-removal is recommended for small populations and isolated stems. Ideally, the plants should be pulled out before they have set seed. The entire rootstock must be pulled out since regeneration from root fragments is possible. Be sure to minimize disturbances to the soil and native vegetative cover. Remove uprooted plants and broken stems from the area since the broken stems can resprout (Rawinski 1982).
REPLACEMENT: Replacement control has been attempted in several wildlife refuges (Balogh 1985, Rawinski 1982). Rawinski (1982) sowed Japanese millet (Echinochloa frumentacea) with L. salicaria and found that the millet seedlings outcompeted the loosestrife seedlings. The millet must be planted immediately after marsh drawdown has occurred. Balogh (1985) found that Japanese millet does not regenerate well and would have to be replanted every year. Balogh (1985) attempted a replacement treatment using native seed. Polygonum lapathifolium was seeded with purple loosestrife and the Polygonum outcompeted the loosestrife. However, the following spring L. salicaria would start growing first due to its overwintering rootstock. Replacement methods would have a very limited application within a natural area, but they may be useful to control or contain loosestrife populations on buffer property.
BIOLOGICAL: Several characteristics of L. salicaria make it an ideal candidate for biological control (USFWS 1987). Batra (et al. 1986) recommends detailed ecological and host-specificity studies for six European species: a cecidomyiid fly whose galling can reduce purple loosestrife foliage by 75% and seed production by 80%; a stem and root boring weevil; two chrysomelids that can cause nearly 50% defoliation; and two weevils that mine ovaries and seeds. The results of Batra et al. (1986) indicated that the chances of successful biological control of L. salicaria in North America are excellent.
The following individuals are familiar with L. salicaria and can suggest control strategies:
Dottie Thompson, Horicon National Wildlife Refuge, Rt. 2, Mayville, Wisconsin 53050. (414) 387-2658.
Rich Henderson, Consultant, Natural Area Management, 2845 Timberlane, Verona, Wisconsin 53593. (608) 845-7065.
John Schwegman, Director, Botany Program, Illinois Dept. Conservation, Springfield, Illinois 62706.
Tom Jackson, Leader, Field Research Station, U.S. Fish and Wildlife Service, P.O. Box 25007, Denver, Colorado 80225.
Jay Rendall, Coordinator, Purple Loosestrife Program, MN Dept of Natural Resources, Box 25, 500 Lafayette Rd, St. Paul, MN 55155.
Management Research Programs: A research project in Wisconsin includes investigations on different methods of control and different herbicide treatments. The ecology of L. salicaria including seed bank buildup is also under investigation. Contact: Rich Henderson, Consultant-Natural Area Management. 2845 Timberlane, Verona, Wisconsin 53593.
Hand cutting purple loosestrife and fertilizing cattails under varying degrees of wetness is being studied at Indiana Dunes National Lakeshore. Contact: Ron Heibert, Chief, Division of Science, 1100 N. Mineral Springs Rd., Porter, Indiana 46304.
Research on the effectiveness of various chemical controls will be conducted in Illinois, pending funding. Contact: John Schwegman, Director, Botany Program, Illinois Dept. Conservation, Springfield, Illinois 62706.
A research project funded by the Metropolitan Council (MN) is being conducted by Hennepin County Park Reserve. Chemical control techniques are to be evaluated for 2 years in control plots. Contact: Tom Hollenhorst, Hennepin County Park Reserve, 3800 Co. Rd. 24, Maple Plain, MN 55359.
The Minnesota Legislative Commission on Minnesota Resources (LMCR) has funded a comprehensive control program over a two year period. The program will inventory purple loosestrife in Minnesota, keep abreast of current contol methods and research, implement a prioritized control program, monitor environmental impact and effectiveness of control, promote public awareness campaigns, and coordinate agencies control efforts within the state. Contact: Jay Rendall, Coordinator, Purple Loosestrife Program, MN Dept of Natural Resources, Box 25, 500 Lafayette Rd, St. Paul, MN 55155.
Management Research Needs:
Biological control methods should be a priority for research. Repeated chemical treatments are costly and the long-term effects on natural systems are not fully understood. Preliminary investigations in Europe have revealed several host-specific insects that keep L. salicaria in check. Further research is warranted. Research is needed to assess the potential productivity of the seed bank. How extensive is the seed bank in a wetland in comparison to the size of the above-ground population? What is the rate of seed buildup? Can the age of a seed bank be determined? What is the viability of purple loosestrife seed? More research is needed on herbicide treatments that will give the most selective application with the least impact to the surrounding competitive vegetation, i.e. wick applications, etc. Available information suggests that research on mechanical treatments will not yield helpful results.
Impacts and Control
Impacts: Purple loosestrife can be highly competitive, often reported as occurring in dense, monospecific stands, with the potential to dominate wetland plant communities where it occurs (see Successional Status) [1,41,65,66,78,129,136,137]. While it is evident that invading purple loosestrife may have harmful impacts on native flora and fauna, more research is needed to clarify the extent of these impacts. Hager and McCoy  and Anderson  provide critical reviews of literature describing purported negative impacts caused by purple loosestrife in North America. Both papers express concern that widespread claims of ecological harm caused by purple loosestrife are largely unproven. In a widely cited review of purple loosestrife literature in North America, Thompson and others  describe encroachment of purple loosestrife around the margins of a waterfowl impoundment in central New York. Their estimates of percent of total plant biomass contributed by purple loosestrife along dike areas of the impoundments describe "dramatic" increases over about a 15-year period. Based on visual estimates of plant biomass, the authors contend that native plant species were displaced, vegetation structure was altered, and habitat quality for nesting waterfowl was seriously degraded. The paper by Thompson and others  demonstrates how untested hypotheses can be perpetuated in the literature until they become widely accepted, without the benefit of experimental analysis . As emphasized by Anderson , "detailed, quantitative data are needed to understand loosestrife's natural history, population dynamics, and impacts on native ecosystems if we are to effectively manage this plant."
Because purple loosestrife has demonstrated strong competitive abilities where it has invaded North American wetland communities, there is concern that it may diminish native plant diversity. For instance, competition with purple loosestrife has been suggested as a contributing factor in the decline of the rare Long's bulrush (Scirpus longii) in Massachusetts . However, studies published to date have failed to demonstrate a deleterious effect of purple loosestrife on native plant diversity. Treberg and Husband  examined the association between purple loosestrife abundance and vascular plant richness along the Bar River in Ontario. Purple loosestrife had been present in this area for at least 12 years and there was a wide range in established plant densities. They found no significant (P<0.05) difference in mean species richness associated with the presence or percent cover of purple loosestrife, and no plant species was significantly (P<0.05) more likely to be found in the absence of purple loosestrife than in its presence. Anderson  showed no significant (P<0.05) correlation between total species richness and either percent cover, genet density or median age of purple loosestrife, even in plots containing 18-20 year old purple loosestrife plants. He suggested areas with apparent purple loosestrife monocultures perhaps had low species richness to begin with, and species richness more likely resulted from habitat heterogeneity rather than the presence of innately competitive species. More research is needed in this area.
Purple loosestrife colonization has been purported to have detrimental effects on birds, based on: a) creation of unsuitable nesting habitat and b) low food potential of purple loosestrife relative to vegetation it displaces. However, published studies and observations indicate impacts on birds are not yet clear. Marsh wrens prefer cattails to purple loosestrife for nesting [101,142]. There is speculation that invasion of riparian areas in Nebraska may have adverse effects on important night-roosting habitat for migratory sandhill cranes. Purple loosestrife invasion is predicted to have detrimental effects on nesting habitat of black terns and canvasbacks in the north-central United States, but this has not been tested . Whitt et al.  found purple loosestrife-dominated habitats had significantly (P=0.003) higher bird densities but significantly (P=0.03) fewer bird species than other habitats. These higher densities were mainly due to increases in populations of a single species, the swamp sparrow.
Purple loosestrife colonization can substantially reduce or eliminate open water in small marsh areas, potentially reducing its usefulness for waterfowl. In areas with substantial seed banks, mudflats that are commonly used as feeding areas by shorebirds are impacted by rapid, dense colonization by purple loosestrife seedlings. Decline in the extent of open water habitats from increased emergent purple loosestrife can retard access to aquatic prey items such as fish and aquatic invertebrates. Important aquatic food plants for wildlife such as pondweeds (Potamogeton spp.) are inhibited under the shade of emergent purple loosestrife . Invading purple loosestrife in coastal British Columbia's Fraser River estuary may have negative effects on detrital food chains .
Thompson and others  have illustrated how muskrats might interact with purple loosestrife in a manner detrimental to muskrats. Muskrats apparently find stems of purple loosestrife much less palatable then those of cattail, but they do cut purple loosestrife stems. As they forage they favor cattail stems, potentially shifting the competitive balance toward the less palatable purple loosestrife. The ability of muskrats to shift the competitive balance between cattails and purple loosestrife was corroborated by Rawinski  from observations of mixed stands where muskrats were present. At a particular site, muskrats removed entire patches of cattail, leaving purple loosestrife the only remaining emergent. Muskrats may further favor purple loosestrife seedling establishment following den construction. This activity can cause substantial soil disturbance that is rapidly colonized by purple loosestrife seedlings during lower summer water levels. Because of their ability to generate new vegetative growth, partially eaten purple loosestrife stems also represent potential new propagules, adding to its competitive advantage . As community composition shifts from cattails to purple loosestrife dominance, habitat quality and subsequent muskrat carrying capacity apparently decline .
Conversion of wetland pasture to predominantly purple loosestrife is believed to reduce forage value for livestock and deer . As purple loosestrife density increases and mature plants produce greater numbers of shoots, the woody nature of purple loosestrife stems diminishes forage value .
Purple loosestrife invasion may be detrimental to production of natural and domestic wild rice in areas of the upper Midwest, particularly in commercial wild rice paddy operations where water level manipulation presents ideal germination conditions. Dense purple loosestrife infestations can also undermine the functionality of drainage waterways, such as irrigation ditches .
Water level manipulations in impoundments have been hindered by threat of purple loosestrife invasion. A 1000-fold increase in acreage containing purple loosestrife was noted over a 23-year period in a central New York wetland and the cause was speculated to be recurrent drawdown of impoundments . In areas managed for waterfowl production, such as many federal and state wildlife refuges, water level drawdowns in impoundments may provide establishment opportunities for purple loosestrife. Drawdowns are often executed to encourage recruitment of plants valuable to waterfowl such as cattails, smartweed (Polygonum spp.) and wild millet (Echinochloa spp.) on exposed soils .
Invading purple loosestrife is being monitored in the middle Snake River corridor in Idaho for effects on stream channel dynamics. Purple loosestrife is colonizing gravel bars under low flow conditions. Once established, it appears able to withstand inundation and flowing water conditions better than native annuals. It is feared that persistent purple loosestrife plants may contribute substantially to sediment trapping, leading to gravel bar aggradation, closure of small channels, and despoiling of secure, predator-free island nesting habitat for local waterfowl .
Control: Land managers concerned about invasive purple loosestrife should focus on eliminating small, recently-established populations before tackling large, well-established populations. Buildup and persistence of purple loosestrife seed in the soil seed bank appears to be the most problematic, long-term obstacle in eradicating, or at least controlling purple loosestrife. Preventing seed production and seed bank accumulation within recently-established stands is a pragmatic goal, especially in the face of limited resources and knowledge [138,139]. Welling and Becker  demonstrated the potential difficulty managers face with attempts to exhaust seed banks in areas where purple loosestrife is well established, although not necessarily monodominant. Because seed dormancy is enforced by burial at relatively shallow (>0.8 inch (2 cm)) depth, and because purple loosestrife seed banks may contain thousands of seeds per square foot at these depths, even successful eradication of extant adult plants and new recruits from near-surface germinants may not suffice for successful long-term control. Even the ability to exhaust near-surface (<0.4 inch (1 cm)) seed banks by promoting germination and removing emergent seedlings is in question.
Any disturbance or management activity that fragments live stem or root tissue is likely to result in the spread, rather than containment of purple loosestrife [23,118]. Live stems that are dislodged and buried can give rise to new shoots via adventitious buds [23,129]. Carp may play an important role where they co-occur with purple loosestrife. Carp eat the roots of purple loosestrife, sometimes until the plants are dislodged and float away. These plants then become potential propagules if they lodge on suitable substrate .
Detection and control efforts may be hindered by purple loosestrife's propensity to occasionally remain dormant for an entire growing season. Some plants fail to generate aboveground shoots during a particular year, but exhibit normal growth from the same rootstock in preceding and following years [42,129].
Prevention: It is important to avoid management activities that may enhance the risk of purple loosestrife invasion and expansion. Examples of mitigative efforts are a) encourage establishment, growth, or perpetuation of native woody cover that might provide enough shade to depress or discourage purple loosestrife, b) minimize water level fluctuations in manipulated wetlands or waterways that might encourage establishment of purple loosestrife seedlings, especially early-season drawdowns that expose bare substrate, and c) avoid any form of stress or disturbance to extant native plant communities in susceptible areas, such as disturbing soil with heavy machinery, and where such activities are unavoidable, monitoring impacted areas to detect invaders .
Periodic, systematic monitoring of susceptible habitats is strongly encouraged . Development of local populations, as expressed by percent biomass constituted by purple loosestrife, is roughly a logistic function through time. Initial rate of spread of local infestations is slowed when extant competition is strong. As a result, early detection and eradication of colonizing plants is highly preferred. Fortunately, early detection is aided by the tall, showy flower stalks and lengthy period of bloom. Once purple loosestrife becomes strongly established, with many (>10) flowering stems per rootstock, multiple clumps forming monospecific patches or stands, and establishment of a seed bank, eradication becomes more expensive, intrusive, and difficult .
Spread of purple loosestrife in natural areas likely has been accelerated by the development, sale and use of various loosestrife cultivars for horticultural purposes. Sale and utilization of ornamental loosestrife cultivars should be curtailed to prevent the risk of further dissemination into previously uncolonized areas. Cultivars are capable of contributing viable seed and pollen to wild populations, and claims of sterile hybrids have been shown to be mainly false [3,74,92].
As with most invasive species, public education plays an important role in preventing establishment and spread of purple loosestrife. Planting of loosestrife cultivars for horticultural purposes should be strongly discouraged. Individuals who frequent areas susceptible to invasion can aid in prevention by washing boots, clothing, equipment, etc. before exiting such areas, and should be encouraged to identify and report potential new infestations to authorities.
Integrated management: A single method may not be effective for long-term control or removal of purple loosestrife. Integrated management involves using several management techniques in a well-planned, coordinated and organized program. Many combinations of control methods can achieve desired objectives. Methods selected for a specific site will be determined by land-use objectives, desired plant community, extent and nature of infestation, environmental factors (nontarget vegetation, habitat types, climate, hydrology, etc.), economics, and effectiveness and limitations of available control techniques [103,114].
Cultural: Seeding of competitive vegetation in areas where bare soil has been exposed may be a useful mitigative measure. This may be especially helpful where presence of seed in the soil seed bank indicates potential for robust purple loosestrife regeneration. Experiments examining the effectiveness of seeding Japanese millet (Echinochloa esculenta) to reduce the impact of purple loosestrife recruitment have shown mixed results [80,140]. In addition to providing competition against purple loosestrife seedlings, Japanese millet may be used by waterfowl and is thought to represent a minimal threat of invasiveness, although it is not native to North America . Seeding native species may provide a desirable postdisturbance community, but explicit tests of the competitive abilities of various native plants when seeded with purple loosestrife are lacking. Seeding of competitors should take place immediately following exposure of soil to maximize their competitive abilities .
Flooding infested areas by raising water levels for extended periods may eliminate purple loosestrife from impoundment sites . Flooding duration is more likely to influence mortality than depth of flooding, but specific guidelines are lacking . Persistent high water conditions can slow the growth and reproductive capacity of purple loosestrife and over several years may eliminate extant stands, but results are variable and interactions with other factors poorly understood . In plots subjected to consistently high water levels (16 inch (40 cm) mean depth)), competition with narrow-leaved cattail significantly (P<0.001) reduced stem densities of purple loosestrife compared with flooded stands where purple loosestrife was the predominant species . More research is needed to determine optimal flooding duration and factors that influence variability in the effect of flooding duration .
Effectiveness of flooding as a control measure may be enhanced by cutting purple loosestrife stems prior to raising water levels . Cut material should always be removed from the site to prevent spread of vegetative propagules. The efficacy of flooding may be influenced by the presence of carp within contiguous waterways, although the ultimate effects are unclear. Carp may reduce purple loosestrife by grazing its roots or enhance its spread by disseminating vegetative propagules . Carp are not native to North America and should not be introduced as a means to control purple loosestrife.
Consistent spring and early-summer flooding may inhibit purple loosestrife seedling establishment [9,137]. Flooding seedlings 0.8 to 4 inches (2-10 cm) tall for 9 weeks at depths up to 12 inches (30 cm) did not significantly (P<0.05) reduce mean stem densities. Most plants continued to grow, if slowly, while submerged, and plants which emerged above the surface quickly resumed rapid growth . Established purple loosestrife plants can survive in deepwater emergent habitat, in part by development of aerenchymous (containing large intercellular air spaces) stem tissue that facilitates gas exchange in aquatic environments.
Several factors may hinder the effectiveness of controlling purple loosestrife by flooding. Managers may be constrained in their ability to manipulate water levels by the geologic profile of the site or by development along its margins. Substantial warm season evaporation can contribute to this problem. Sustained high water levels may be detrimental to desirable native emergent or shoreline vegetation. Once purple loosestrife has been killed, managers should consider species composition within the remnant seed bank, and the ensuing colonizing community, when water levels have been reduced. It is likely that purple loosestrife seedlings will recolonize the newly exposed soil and further management may be inevitable.
Physical/mechanical: Cutting stems or removing flower heads prior to seed dissemination can prevent local seed bank accumulation. Late-summer cutting appears to reduce vegetative growth more effectively than mid-summer treatments. However, cutting stems is unlikely to prevent perennial stem growth [46,102]. Cutting flower heads may be useful in preventing further seed production when primary control activities, such as herbicide application, require more than 1 season to completely eradicate purple loosestrife . Cutting purple loosestrife stems underwater at various times in summer was ineffective .
Digging or hand-pulling plants is recommended for early infestations or a few scattered plants. Digging or pulling young plants in recently colonized areas can be effective in preventing establishment of dense, intractable stands and buildup of substantial seed banks. Early detection is important since established plants may rapidly become too large and deep-rooted for easy removal [102,129]. Because growing points of the plant are located on the root crown, removal of as much rootstock as possible is strongly encouraged [23,46]. Pulling entire plants is easiest when the soil is wet [102,131]. All pulled plant material should be removed from the site to prevent vegetative reproduction from discarded fragments . Spot spraying individual plants with herbicide may be less time and labor intensive when infestations become too large for removal by pulling or digging .
Fire: See Fire Management Considerations.
Biological: The objective of biological control is to re-establish ecological relationships that have evolved between purple loosestrife and its native predators in order to suppress invasive populations and reduce harmful impacts. Potential advantages of biological control are cost effectiveness at large scales, sustainability, and benign effects in the nontarget environment [22,131]. The Nature Conservancy's Weed Control Methods Handbook provides a comprehensive discussion of considerations and safety issues in developing and implementing a biological control program.
Plant communities where purple loosestrife is found are similar in North America and Europe. Because native insect herbivory inhibits purple loosestrife performance in Europe, it is hoped introductions of European insect herbivores may work to reduce the competitiveness of purple loosestrife in North America, while releasing native plants from suppression [18,19].
The following table lists non-native insects released in North America to control purple loosestrife:
|Control Agent||Mode of Action||Release Sites|
|Galerucella calmariensis (beetle)||Larvae and adults feed on foliage and flowers||MB, ON|
|Galerucella pusilla (beetle)||Larvae and adults feed on foliage and flowers ||MB, ON, WA [29,31,97]|
|Hylobius transversovittatus (weevil)||Larvae and adults feed on roots ||WA |
|Nanophyes marmoratus (weevil)||Larvae feed on flowers and adults feed on foliage and flowers ||MB |
Galerucella beetles have been the most effective biocontrol agents used against purple loosestrife in North America thus far [29,62,97]. G. calmariensis and G. pusilla are similar in appearance and habit and are most effective when released together, and both species appear to be unaffected by exposure to the herbicides glyphosate and triclopyr [75,76]. Because of "dramatic" success at some Galerucella release sites, release of other agents should focus on sites where Galerucella have been ineffective. In Europe, H. transversovittatus herbivory on purple loosestrife is strongest in the northern range of the plant, indicating that higher latitude sites may be a good choice for its release in North America .
Myzus lythri, a European aphid that has probably been present in the Eastern United States since the early 1930's, might become an effective biological control agent. It has a host-alternating life cycle, utilizing loosestrife and Epilobium spp. in summer and Prunus spp. as primary hosts the rest of the year. Populations of M. lythri could be manipulated to impact local purple loosestrife populations by mass-rearing bugs for targeted early-spring release and/or by planting Prunus spp. near targeted sites .
Research examining the potential use of pathogenic fungi as biocontrol agents is ongoing .
Chemical: A variety of herbicides are effective at controlling purple loosestrife in infested areas. Below is a list of herbicides that have been used effectively against purple loosestrife in North America, as well as a brief discussion of important considerations regarding their use. This is not intended as an exhaustive review of chemical control methods. For more detailed information regarding appropriate use of herbicides in natural areas against this and other invasive plant species, see The Nature Conservancy's Weed Control Methods Handbook.
|2,4-D [13,90,118,140]||Mixed results against purple loosestrife; harmful to dicots, but little impact on neighboring monocots|
|Triclopyr [12,38,61,89,118]||Generally effective at killing purple loosestrife; results are variable with spray volume; selective against dicots|
|Glyphosate [12,80,102,104,118,122,131]||Highly effective against purple loosestrife; specific formulations available for use in aquatic environments; also damages or kills most other plants which it contacts|
|Imazapyr ||Effective against purple loosestrife; negatively impacts cattail|
A serious challenge to controlling purple loosestrife infestations with herbicides is preventing its re-establishment from the seed bank. In the presence of large purple loosestrife seed banks, removal of a considerable fraction of extant vegetation (weed or otherwise) can result in a dense monoculture of purple loosestrife seedlings. The result may be a worse infestation than was originally present . Broadcast application of broad-spectrum herbicides, such as glyphosate, will likely result in widespread exposure of bare substrate and a dense, monotypic stand of purple loosestrife seedlings . By carefully targeting glyphosate spray application to only purple loosestrife, damage to nontarget plants can be minimized. Continued careful treatments over several years can eventually reduce dense populations of purple loosestrife to minimal levels while promoting native plants [104,122]. Native plants are not just inherently valued, but can also provide competition against inevitable purple loosestrife recruitment from existing seed banks .
An apparent tradeoff exists when determining the best time to treat adult stands with herbicides. Managers must attempt to balance preventing seed production in established plants with treatments early in the growing season and preventing establishment of a viable new stand of purple loosestrife seedlings by delaying treatments long enough to inhibit recruitment. By conducting herbicide treatments on adult plants late in the growing season, newly established seedlings may not develop sufficiently to survive winter . Late-summer herbicide application also appears to reduce negative effects on desirable native plants . Rawinski  found that glyphosate application during late-bloom (mid-August in central New York) period, compared with late-vegetative (mid-June) period, resulted in fewer loosestrife seedlings the following season and increased presence of naturally established, beneficial plants such as shallow sedge (Carex lurida), rice cutgrass (Leersia oryzoides), smartweed and marsh seedbox (Ludwigia palustris). Late-season application of glyphosate in Minnesota wetlands tended to reduce cattail mortality compared with mid-summer treatments, perhaps because the onset of cattail senescence reduced herbicide uptake .
Another tradeoff exists between spray volume and target vs. nontarget effects. Purple loosestrife in Wisconsin was examined for response to variation in spray coverage of glyphosate (Rodeo at 1.5%). Individual genets were spot treated in mid-September and received either low (10-25% leaf area coverage), medium (40-60%), or high (75-90%) dosages. Reduction in adult purple loosestrife density was greatest in the high dosage treatment (90-100% reduction) and lowest in the low dosage treatment (75-90% reduction). Surviving purple loosestrife plants in all treatments were greatly reduced in size and vigor. Because glyphosate is nonselective in its effect, survival of nontarget vegetation was also closely related to dosage. High dosage treatment resulted in dense stands of purple loosestrife seedlings with little to no interspecific competition. In contrast, low dosage treatment resulted in high survival rates of desirable perennials and greatly reduced germination of purple loosestrife seedlings. Effective long-term control of purple loosestrife with glyphosate might best be achieved using low-dosage spot applications and conducting followup treatments in subsequent years as necessary .
To minimize non-target effects, managers in Michigan have developed a cut-and-herbicide method for purple loosestrife control. They propose cutting plants high on the stem (just below infloresence), allowing them to continue growing and better absorb the applied herbicide throughout the entire plant. Cutting too low apparently risks forcing the plant to "give up" on the leader and instead producing new ramets from the rootstock. Sponge applicators have been developed that limit contact between chemicals and nontarget plants . These methods may be particularly useful in areas where mitigation of damage to indigenous species is important. Encouraging competition from extant native plants often helps reduce the vigor of invasives. For more detailed information regarding these methods, see Tu  and the TNC Weed Control Methods Handbook.
Prevention and Control
Please contact your local agricultural extension specialist or county weed specialist to learn what works best in your area and how to use it safely. Always read label and safety instructions for each control method. Trade names and control measures appear in this document only to provide specific information. USDA, NRCS does not guarantee or warranty the products and control methods named, and other products may be equally effective.
An important consideration in controlling purple loosestrife is its prolific seed production, the ease with which seeds are dispersed, and their ability to remain viable for several years. Also, this plant can spread vegetatively by resprouting from stem and rootstock cuttings. Other considerations in selecting control methods are their detrimental effects on native species and the possibility for reinvasion by purple loosestrife or other exotic species. In addition, native plants of similar appearance should not be subjected to control. Purple loosestrife may superficially resemble plants of the mint family or species of the genera Epilobium and Liatris. Proper identification is an important consideration in controlling exotic loosestrife.
In natural areas, it may be more feasible to contain populations of purple loosestrife than control them. Large populations extending over one hectare or more will be difficult to eradicate. Containing them may be more feasible. Removing plants or applying herbicides to ones extending beyond the main population can accomplish this. If loosestrife cannot be eradicated, efforts should then concentrate on keeping it from invading the highest quality areas (Butterfield et al., 1996.
Manual, Mechanical, and Replacement: Mowing, burning, and flooding are largely ineffective. Cutting followed by flooding so that cut plant stalks are completely immersed has shown some success. However, flooding may encourage the spread of purple loosestrife seed present in the soil and may result in the regeneration of new plants from stem fragments. Mature plants can withstand short-term immersion. Burning is largely ineffective and it may also stress native plants and subsequently enhance loosestrifes’ competitive advantage (Butterfield et al., 1996).
Hand removal is effective for small populations and isolated plants. Younger plants (one to two years old) can be pulled by hand. Plants should be removed, prior to seed set, with minimal disturbance to the soil. Removal after seed-set will scatter the seeds. The entire rootstock must be pulled out because of the potential for regeneration from root fragments. A hand cultivator or similar implement will be helpful for older plants, especially those in deep organic soils. Uprooted plants and broken stems need to be removed from the site since such fragments can re-sprout. Bagging plants for removal will prevent their spread along the exit route. Follow-up treatments are recommended for three years after plants are removed. Clothing and equipment used during plant removal should be cleaned to remove contaminating seeds.
Replacement control has been attempted in several wildlife refuges. Research has shown that Japanese millet (Echinochloa frumentacea Link) seedlings outcompete purple loosestrife seedlings. The millet must be planted immediately after marsh drawdown and replanted each year because it does not regenerate well. Replacement seeding trials using native pale smartweed (Polygonum lapathifolium L.) showed that it also out-competed purple loosestrife. Replacement methods have obvious limited application in natural areas, but they may provide control of loosestrife populations on bordering property (Butterfield et al. 1996).
Herbicide Control: Various chemical treatments have been used on purple loosestrife with varying success. Many herbicides are not specific to purple loosestrife and may not be specifically licensed for such use. Label directions for application and use according to local, state, and federal regulations must always be observed.
In areas with populations exceeding 100 plants (up to 1.6 ha in size) where hand-pulling is not feasible, application of a glyphosate herbicide to individual purple loosestrife plants provides effective control Glyphosate is available under the trade names Roundup® and Rodeo®. Rodeo is registered for use over open water and is the most commonly used herbicide to control purple loosestrife. Glyphosate is nonselective and can kill desirable plants associated with loosestrife if applied carelessly. Application to the tops of plants alone can be effective and limits exposure of non-target species (Butterfield et al. 1996).
Herbicide treatment should be conducted as early as possible during the manufacturer's recommended time of application in order to kill the plants and prevent seed production. Application is most effective when plants have just begun flowering. Timing is important because seed set can occur if plants are in mid- to late flower. Where possible, the flower heads should be cut, bagged, and removed from the site prior to application to prevent seed set. Rodeo applied as a 1.5% solution (2 oz. Rodeo/gallon clean water) with the addition of a wetting agent, as specified on the label has been shown to provide control. Another option, which may be more effective, is to apply glyphosate twice during the growing season. The plants should be sprayed as described above when flowering has just started and a second time two to three weeks later (Butterfield et al. 1996).
Application of ghyphosate from a vehicle-mounted sprayer is generally necessary in areas with extensive stands of purple loosestrife. The most effective control can be achieved by beginning treatment at the periphery of large patches and working toward the center in successive years. This technique allows native vegetation to re-invade the treated area as the loosestrife in eliminated (Butterfield et al. 1996).
A combination of 2,4-D and Banvel® (dicamba) has been used on a limited basis. This formulation is broadleaf specific and apparently would not hurt the dominants if sprayed in a cattail marsh or communities dominated by rushes, sedges, and grasses. Spraying produces good control once loosestrife has reached 10-15% of its mature growth. Treatment is more effective if repeated once during the growing season (Butterfield et al. 1996).
Biological Control: Several biological control agents have the potential to aid in the control of purple loosestrife. Of 120 species of phytophagous insects associated with purple loosestrife in its natural range in Europe, 14 species were considered host-specific to the target plant. From this group, six species have been selected as the most promising for biological control. These species were a root-mining weevil, Hylobius transversovittatus Goeze, which attacks the main storage tissue of purple loosestrife; two leaf-eating beetles, Galerucella calmariensis L., and G. pusilla Duftschmid, which are capable of completely defoliating the plant; two flower-feeding beetles, Nanophyes marmoratus Goeze and N. brevis Boheman, which severely reduce seed production; and a gall midge, Bayeriola salicariae Kieffer, which similarly reduces seed production by attacking the flower buds. Five of the six species are found throughout its range in Europe and the sixth, N. brevis, is restricted to southern Europe (Malecki et al. 1993; Weedin et al. 1996).
The most promising insects appear to be the root-mining weevil, H. transversovittatus, and the two leaf-eating beetles, G. calmariensis and G. pusilla, because of their broad geographic ranges and the amount of damage done to the host plant. In June of 1992, all three species were approved by USDA, APHIS for introduction into the United States. The insects were released in New York, Pennsylvania, Maryland, Virginia, Minnesota, Oregon, and Washington. Releases were also approved in Canada (Malecki et al. 1993).
The two Galerucella species successfully over-wintered and began oviposition at all release sites. The other species, H. transversovittatus, was proving more difficult to establish, because of its long life cycle and low fecundity. The investigators predict that all three species will become established throughout the North American range of purple loosestrife. Furthermore, H. transversovittatus is expected to have the greatest negative impact to L. salicaria. However, a combination of various phytophagous insects will provide greater control than any one species. Control of purple loosestrife will be achieved more rapidly in mixed plant communities where competition for space and nutrients is greater. A reduction in the abundance of purple loosestrife to approximately 10% of its current level over about 90% of its range is expected (Malecki et al. 1993).
In order to evaluate the potential of fungus pathogens to control purple loosestrife, a survey was conducted on fungi associated with that plant. During the three year study, 5265 fungal isolates were obtained. Thirty-one taxa were found that had not previously been reported from purple loosestrife. Tests for the pathogenicity to purple loosestrife are being tested (Nyvall 1995).
Relevance to Humans and Ecosystems
Purple loosestrife stands may provide cover habitat for wood ducks , ring-necked pheasants and cottontail rabbits .
Importance to Livestock and Wildlife
More info for the term: swamp
Purple loosestrife shoots may be grazed by white-tailed deer [2,102], muskrat [2,129], and rabbits [2,113], but extent of mammal herbivory is sometimes difficult to determine due to rapid regrowth of multiple new stems from browse points. In a mixed stand of purple loosestrife and cattail, foraging muskrats were observed to occasionally cut stems of purple loosestrife but preferentially fed on roots and overwintering shoots of cattail .
While purple loosestrife invasion is often reported as detrimental to wetland-bird habitat, some evidence indicates little to no harmful effect. American coot, pied-billed grebe, black-crowned night heron, American goldfinch and gray catbird have all been observed nesting in purple loosestrife stands [2,102]. Red-winged blackbirds preferentially nest in purple loosestrife over cattails [101,142]. American goldfinch construct nests in purple loosestrife, utilizing the relatively stable stalks to attach nests above the ground or water surface . Pied-billed grebes use dead purple loosestrife stems as nest substrate in habitat with standing and emergent vegetation . In a 2-year survey of birds in wetlands surrounding Lake Huron's Saginaw Bay in eastern Lower Michigan, swamp sparrow nests were most abundant in areas of purple loosestrife dominance .
Although purple loosestrife, with its tiny seeds, has been assumed to provide little to no food for birds , there are several reports of ducks and red-winged blackbirds consuming purple loosestrife seeds , and a report of damage to experimental seedling plots in England caused by ring-necked pheasants and pigeons .
Other uses and values
Noxious and highly invasive.
Ethnobotanic: Immigrants might have deliberately introduced L. salicaria for its value as a medicinal herb in treating diarrhea, dysentery, bleeding wounds, ulcers, and sores, for ornamental purposes, or as a source of nectar and pollen for beekeepers (Hayes 1979; Jones 1976; Malecki et al. 1993; Stuckey 1980). In states where it is permitted, purple loosestrife continues to be promoted by horticulturists for its beauty as a landscape plant and for bee-forage. Purple loosestrife has been of interest to beekeepers because of its nectar and pollen production. However, honey produced from it is apparently of marginal quality (Feller-Demalsy & Parent 1989).
Horticultural: Horticultural cultivars of purple loosestrife (Lythrum spp.) were developed in the mid-1900s for use as ornamentals. Initially, these were thought to be sterile, and therefore safe for horticultural use. Recently, under greenhouse conditions, experimental crosses between several cultivars and wild purple loosestrife and the native L. alatum produced hybrids that were highly fertile (Ottenbreit 1991; Ottenbreit & Staniforth 1994). Comparable, subsequent experiments performed under field conditions produced similar results, suggesting that cultivars of purple loosestrife can contribute viable seeds and pollen that can contribute to the spread of purple loosestrife (Lindgren & Clay 1993). Ottenbreit & Staniforth (1994) indicate that such results suggest the need to prohibit cultivars of this species.
Noxiousness: Purple loosestrife grows most abundantly in parts of Canada, the northeastern United States, the Midwest, and in scattered locations in the West. Although this species tolerates a wide variety of soil conditions, its typical habitat includes cattail marshes, sedge meadows, and bogs. It also occurs along ditch, stream, and riverbanks, lake shores, and other wet areas. In such habitats, purple loosestrife forms dense, monospecific stands that can grow to thousands of acres in size, displacing native, sometimes rare, plant species and eliminating open water habitat. The loss of native species and habitat diversity is a significant threat to wildlife, including birds, amphibians, and butterflies, that depend on wetlands for food and shelter. Purple loosestrife monocultures also cause agricultural loss of wetland pastures and hay meadows by replacing more palatable native grasses and sedges (Mal et al. 1992; Thompson et al. 1987).
Having a noxious weed designation in some states prohibit its importation and distribution, but it is readily available commercially in many parts of the country. Lythrum salicaria has been labeled the “purple plague." because of its epidemic devastation to natural communities. The species is included on the Nature Conservancy’s list of “America’s Least Wanted -The Dirty Dozen” (Flack & Furlow 1996).
Impact/Vectors: Naturalized purple loosestrife was relatively obscure from the time of its introduction into North America in the early 1800s (Pursh 1814) until 1930, when a significant increase in populations invading wetlands and pastures was documented (Strefeler et al. 1996b). Reasons for the apparent sudden colonization and spread of this species include the disturbance of natural systems by human activities including agricultural settlement, construction of transport routes such as canals, highways, and perhaps, nutrient increases to inland waters (Mal et al. 1992; Malecki et al. 1993). Absence of natural enemies and ornamental use are other possible causes for purple loosestrife’s rapid expansion in North America (Thompson et al, 1987). Recently created irrigation systems in many western states have supported further establishment and spread of L. salicaria (Malecki et al. 1993).
The acquisition of adaptive characteristics from native species of Lythrum may have enhanced purple loosestrife’s invasive success. It will hybridize with Lythrum alatum, a widespread, native North American species, in natural settings. Under certain circumstances fertile hybrids are produced that can cross with weedy purple loosestrife. Such interspecific hybrids could serve as a “hybrid bridge” for the transfer of adaptive traits from native L. alatum into weedy populations of purple loosestrife (Anderson & Ascher 1993; Strefeler et al. 1996b).
North American naturalized populations of purple loosestrife often form monospecific stands, whereas, in its native Eurasian habitat the species comprises 1-4% of the vegetative cover (Batra et al. 1986; Strefeler et al. 1996b). Purple loosestrife causes annual wetland losses of about 190,000 hectares in the United States (Thompson et al. 1987; Mal et al. 1997). The species is most abundant in the Midwest and Northeast where it infests about 8,100 hectares in Minnesota, 12,000 ha in Wisconsin, over 12,000 ha in Ohio, and a larger area in New York State. Recent distributional surveys document the occurrence of monocultures in every county in Connecticut, where it has been found in 163 wetland locations (Ellis and Weaver 1996; Ellis 1996). At the Effigy Mounds National Monument (EFMO), combined populations of purple loosestrife cover an area of 5 to 10 hectares growing in regularly disturbed sites. This species has a major visual impact on the vegetation of EFMO, and it has the potential to invade and replace native communities endangering the areas' primary resources. (Butterfield et al. 1996). In response to the alarming spread of this exotic species, at least 13 states (e.g., Minnesota, Illinois, Indiana, Ohio, Washington, and Wisconsin) have passed legislation restricting or prohibiting its importation and distribution (Malecki et al. 1993; Strefeler et al. 1996b).
Numerous studies demonstrate the aggressive and competitive nature of purple loosestrife. Fernald (1940) reported a loss of native plant diversity in the St. Lawrence River floodplain following the invasion of purple loosestrife and another exotic, Butomus umbellatus L. Gaudet and Keddy (1988) report declining growth for 44 native wetland species after the establishment of Lythrum. Among the species tested, Keddy (1990) found that purple loosestrife was the most competitive. His hierarchical rank, arranged from most to least competitive, illustrates the dominance of this invasive weed over many common natives: Lythrum>Cyperus>Juncus> Eleocharis> Mimulus>Verbena. In the Hamilton Marshes adjacent to the Delaware River, annual above-ground production of L. salicaria far exceeded all other plant species’ production combined.
Purple loosestrife provides little food, poor cover, and few nesting materials for wildlife (Mann 1991). Waterfowl nesting becomes more difficult as clumps of L. salicaria restrict access to open water and offer concealing passageways for predators such as foxes and raccoons (Mal et al. 1992). Non-game species, including black terns and marsh wrens, also lose nesting sites when purple loosestrife infests their normal habitats. Balogh and Bookhout (1989a) report that dense stands of purple loosestrife provide poor waterfowl and muskrat habitat. Red-wing blackbirds appear to be the only species to cope with changes in wetlands caused by purple loosestrife (Balogh and Bookhout 1989a). In many areas where L. salicaria populations have increased, wildlife species have declined. While some studies may fail to demonstrate cause and affect relationship, they firmly establish circumstantial evidence implicating that Lythrum’s invasion is responsible for major changes in wetland communities (Mal et al. 1992).
Purple loosestrife prefers moist, highly organic soils but can tolerate a wide range of conditions. It grows on calcareous to acidic soils, can withstand shallow flooding, and tolerates up to 50% shade. Purple loosestrife has low nutrient requirements and can withstand nutrient poor sites. Under experimental, nutrient-deficient conditions, the root/shoot ratio increased and provided purple loosestrife with a competitive advantage over the native species Epilobium hirsutum. Survival and growth of L. salicaria was greatly improved by fertilizer treatment and greater spacing between plants. Such results suggest that excessive use of fertilizers and the release of phosphates, nitrates, and ammonia into the environment has enhanced the success of Lythrum (Mal et al., 1992; Shamsi and Whitehead, 1977a and b).
Purple loosestrife flowers from July until September or October. Flowering occurs 8-10 weeks after initial spring growth. The lowermost flowers of the inflorescence open first and flowering progresses upward. The capsules mature in the same sequence and the lowermost will ripen and disperse its seeds while flowering is still occurring further up the inflorescence (Butterfield et al. 1996). Thompson et al. (1987) estimated that on average, a mature plant produces about 2,700,000 seeds annually. Purple loosestrife seeds are mostly dispersed by water, but wind and mud adhering to wildlife, livestock, vehicle tires, boats, and people serve also as agent. Seeds are relatively long-lived, retaining 80% viability after 2-3 years of submergence (Malecki 1990). Welling & Becker (1990) investigated seed bank dynamics in three wetland sites in Minnesota and noted a mean density of 410,000 seeds per square meter in the top 5 cm of soil, which was more than all other species combined.
Spring-germinated seedlings have a higher survival rate than summer-germinated seedlings. Seedlings that germinate in the spring will flower the first year, whereas, summer-germinated seedlings develop only five or six pairs of leaves before the end of the growing season. Since its seeds are small, weighing about 0.06 mg each and carry little food reserves, germination must occur under conditions where photosynthesis can occur immediately. A strong taproot develops quickly in seedlings and persists throughout the life of the plant. The aerial shoots die in the fall and new shoots arise the following spring from buds on the rootstocks. Shoots destroyed by fire, herbicides, or mechanical removal can also regenerate from the rootstock. As plants mature, they produce more and more aerial shoots forming very dense clumps of growth. Purple loosestrife can spread vegetatively by resprouting from stem cuttings and from regeneration of pieces of root stock (Mal et al. 1992). Rhizomatous growth is insignificant in purple loosestrife (Shamsi & Whitehead 1974a; Thompson et al. 1987).
Stewardship Overview: Monitor natural areas for the presence of L. salicaria. Maintain preserves so that purple loosestrife cannot invade and flourish. For small infestations, eradication is possible with spot applications of glyphosate herbicides. Monitor the containment and control procedures.
Current methods for eradicating large, dense populations of loosestrife are not totally effective. Mechanical contol methods are ineffective, and the herbicide most effective is non-selective. Realistically, the long-term control of large populations may require biological controls and/or better herbicides, but their development is at least several years away. Therefore, containment and minimizing seed production are the present contol objectives for large dense populations. (MN DNR 1987)
Ecological Threat in the United States
Purple loosestrife adapts readily to natural and disturbed wetlands. As it establishes and expands, it outcompetes and replaces native grasses, sedges, and other flowering plants that provide a higher quality source of nutrition for wildlife. The highly invasive nature of purple loosestrife allows it to form dense, homogeneous stands that restrict native wetland plant species, including some federally endangered orchids, and reduce habitat for waterfowl.
Ecological Threat in the United States
Lythrum salicaria (purple loosestrife) is a flowering plant belonging to the family Lythraceae. It should not be confused with other plants sharing the name loosestrife that are members of the family Primulaceae. Other names include spiked loosestrife, or purple lythrum.
Lythrum salicaria is a herbaceous perennial plant, that can grow 1–2 m tall, forming clonal colonies 1.5 m or more in width with numerous erect stems growing from a single woody root mass. The stems are reddish-purple or red to purple and square in cross-section. The leaves are lanceolate, 3–10 cm long and 5–15 mm broad, downy and sessile, and arranged opposite or in whorls of three.
The flowers are reddish purple, 10–20 mm diameter, with six petals (occasionally five) and 12 stamens ( one stamen has up to 3,000 seeds), and are clustered tightly in the axils of bracts or leaves; there are three different flower types, with the stamens and style of different lengths, short, medium or long; each flower type can only be pollinated by one of the other types, not the same type, thus ensuring cross-pollination between different plants.
The fruit is a small 3–4 mm capsule containing numerous minute seeds. Flowering lasts throughout the summer. When the seeds are mature, the leaves often turn bright red through dehydration in early autumn; the red colour may last for almost two weeks. The dead stalks from previous growing seasons are brown.
L. salicaria is very variable in leaf shape and degree of hairiness, and a number of subspecies and varieties have been described, but it is now generally regarded as monotypic with none of these variants being considered of botanical significance. The species Lythrum intermedium Ledeb. ex Colla is also now considered synonymous.
Found in ditches, wet meadows and marshes and along sides of lakes.
A number of insects use Lythrum salicaria as a food resource.
The black-margined loosestrife beetle Galerucella calmariensis is a brown beetle with a black line on its thorax. The adult feeds on the leaves of the plant, producing characteristic round holes. Its larvae destroy tender leaf buds and strip the tissue from the leaves. The golden loosestrife beetle Galerucella pusilla is nearly identical to G. calmariensis, but usually lacks the black thoracic line. Its feeding habits are also quite similar to the other leaf beetle.
The loosestrife root weevil Hylobius transversovittatus is a large red nocturnal weevil, which spends its nights feeding on leaves and leaf buds. The larvae emerge from their eggs and immediately burrow into the root of the plant, which they feed on continuously for over a year. This root damage stunts the plant's growth and ability to create seeds. If several larvae inhabit the same root, the plant can be killed.
The loosestrife flower weevil Nanophyes marmoratus is a tiny weevil which lays a single egg in each flower. When the larvae emerge they eat the flowers' ovaries, and the plant is unable to create seeds. The larvae usually proceed to hollow out the flower buds and use them as safe places to pupate.
Cultivation, uses, and impact
It has been used as an astringent medicinal herb to treat diarrhea and dysentery; it is considered safe to use for all ages, including babies. It is also cultivated as an ornamental plant in gardens, and is particularly associated with damp, poorly drained locations such as marshes, bogs and watersides. However, it will tolerate drier conditions. The flowers are showy and bright, and a number of cultivars have been selected for variation in flower colour, including:-
- 'Atropurpureum' with dark purple flowers
- 'Brightness' with deep pink flowers
- 'Feuerkerze' with rose-red flowers has gained the Royal Horticultural Society's Award of Garden Merit
- 'Happy' with red flowers on a short (60 cm) stem
- 'Purple Spires' with purple flowers on a tall stem
- 'Roseum Superbum' with large pink flowers.
As an invasive species
The purple loosestrife has been introduced into temperate New Zealand and North America where it is now widely naturalised and officially listed in some controlling agents. Infestations result in dramatic disruption in water flow in rivers and canals, and a sharp decline in biological diversity as native food and cover plant species, notably cattails, are completely crowded out, and the life cycles of organisms from waterfowl to amphibians to algae are affected. A single plant may produce up to 2.7 million tiny seeds annually. Easily carried by wind and water, the seeds germinate in moist soils after overwintering. The plant can also sprout anew from pieces of root left in the soil or water. Once established, loosestrife stands are difficult and costly to remove by mechanical and chemical means.
Plants marketed under the name "European wand loosestrife" (L. virgatum) are the same species despite the different name. In some cases the plants sold are sterile, which is preferable.
In North America, purple loosestrife may be distinguished from similar native plants (e.g. fireweed Epilobium angustifolium, blue vervain Verbena hastata, Liatris Liatris spp., and spiraea (Spiraea douglasii) by its angular stalks which are square in outline, as well by its leaves, which are in pairs that alternate at right angle and are not serrated.
Purple loosestrife provides a model of successful biological pest control. Research began in 1985 and today the plant is managed well with a number of insect specs that feed on it. Five species of beetle use purple loosestrife as their natural food source and they can do significant damage to the plant. The beetles used as biological control agents include two species of leaf beetle: Galerucella calmariensis and Galerucella pusilla, and threeies of weevil: Hylobius transversovittatus, Nanophyes breves, and Nanophyes marmoratus. Infestations of either of the Galerucella species is extremely effective in wiping out a stand of purple loosestrife, defoliating up to 100% of the plants in an area. The moth Ectropis crepuscularia is polyphagous and a pest species itself, and unsuitable for biological control. used as biological control agents include two species of leaf beetle: Galerucella calmariensis and Galerucella pusilla, and threeies of weevil: Hylobius transversovittatus, Nanophyes breves, and Nanophyes marmoratus. Infestations of either of the Galerucella species is extremely effective in wiping out a stand of purple loosestrife, defoliating up to 100% of the plants in an area. The moth Ectropis crepuscularia
- Flora of NW Europe: Lythrum salicaria
- Flora of China: Lythrum salicaria
- Blamey, M. & Grey-Wilson, C. (1989). Flora of Britain and Northern Europe. ISBN 0-340-40170-2
- Clapham, A.R., Tutin, T.G. and Warburg, R.F. 1968. Excursion Flora of the British Isles. Cambridge University Press. ISBN 0 521 04656 4
- Flora Europaea: Lythrum salicaria
- Med-Checklist: [ Lythrum salicaria]
- Australian Plant Names Index: Lythrum salicaria
- Webb, D.A., Parnell, J. and Doogue, D. 1996. An Irish Flora. Dundalgan Press (W.Tempest) Ltd, Dundalk.ISBN 0-85221-131-7
- Plants for a Future: Lythrum salicaria
- "RHS Plant Selector - Lythrum salicaria 'Feuerkerze'". Retrieved 26 June 2013.
- Huxley, A., ed. (1992). New RHS Dictionary of Gardening. Macmillan ISBN 0-333-47494-5.
- "Non-native Invasive Freshwater Plants - Purple Loosestrife (Lythrum salicaria)". Retrieved 6 June 2014.
- Wilson, L. M., Schwarzlaender, M., Blossey, B., & Randall, C. B. (2004). Biology and Biological Control of Purple Loosestrife. Morgantown, WV: USDA Forest Health Technology Enterprise Team.
14^ Kenneth Graham, The Wind In The Willows: Purple Loosestrife
Names and Taxonomy
Purple loosestrife will hybridize with
European wand loosestrife (Lythrum virgatum) and winged loosestrife
(Lythrum alatum) [3,92]. A
number of different horticultural cultivars have been developed from purple
loosestrife and wand
loosestrife. Although some are purported to be sterile, crosses within and
between cultivars and wild Lythrum spp. are often compatible, and
identification of cultivars and crosses is problematic [92,118].
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