Calvin F. Bey
American elm (Ulmus americana), also known as white elm, water elm, soft elm, or Florida elm, is most notable for its susceptibility to the wilt fungus, Ceratocystis ulmi. Commonly called Dutch elm disease, this wilt has had a tragic impact on American elms. Scores of dead elms in the forests, shelterbelts, and urban areas are testimony to the seriousness of the disease. Because of it, American elms now comprise a smaller percentage of the large diameter trees in mixed forest stands than formerly. Nevertheless, the previously developed silvical concepts remain basically sound.
Range and Habitat in Illinois
Regularity: Regularly occurring
Regularity: Regularly occurring
Global Range: Throughout the eastern U.S., and along riparian habitat in the Great Plains.
eastern North America . Its range extends from southern Newfoundland
westward through southern Quebec and Ontario, northwest through Manitoba
into eastern Saskatchewan, then south on the upper floodplains and
protected slopes of the Dakotas. It is found in the canyons and
floodplains of northern and eastern Kansas and in eastern Oklahoma and
central Texas. American elm is common along the Gulf Coast and east
into central Florida [9,7,29,43].
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):
16 Upper Missouri Basin and Broken Lands
Occurrence in North America
KY LA ME MD MA MI MN MS MO NE
NH NJ NY NC ND OH OK PA RI SC
SD TN TX VT VA WV WI MB NB NF
ON PQ SK
The native range of American elm.
USA: AL , AR , CT , DE , FL , GA , IL , IN , IA , KS , KY , LA , ME , MD , MA , MI , MN , MS , MO , MT , NE , NH , NJ , NY , NC , ND , OH , OK , PA , RI , SC , SD , TN , TX , VT , VA , WV , WI , WY , DC (NPIN, 2008)
Canada: MB , NB , NS , ON , PE , QC , SK (NPIN, 2008)
Native Distribution: N.S., s. Man & s.e. Sask. & Crook Co. WY, s. to FL & c. TX (NPIN, 2008)
USDA Native Status: L48(N), CAN(N) (NPIN, 2008)
American elm is a deciduous, fast-growing, long-lived tree which may
reach 175 to 200 years old with some as old as 300 years [5,27,53]. In
dense forest stands, American elm may reach 100 to 200 feet (30-36 m) in
height and 48 to 60 inches (122-152 cm) in d.b.h. Heights of 80 feet
(24 m) are common on medium sites but on very wet or very dry soils, the
species is often 40 to 60 feet (12-18 m) tall at maturity [5,44,54]. In
the forest American elm often develops a clear bole 50 to 60 feet (15-18
m) in length. Open-grown trees fork 10 to 20 feet (3-6 m) from the
ground with several erect limbs forming a wide, arching crown [29,56].
The alternate, double-toothed leaves are 2 to 5 inches (5-10 cm) long
and 1 to 3 inches (2.5-7.5 cm) wide. The dark gray bark is deeply
furrowed (9,15). The perfect flowers are borne in dense clusters of
three or four fascicles. The fruit is a samara consisting of a
compressed nutlet surrounded by a membranous wing [7,29].
The root system of American elm varies according to soil moisture and
texture. In heavy, wet soils the root system is widespreading, with
most of the roots within 3 to 4 feet (1.0 - 1.2 m) of the surface. On
drier soils, American elm develops a deep taproot .
Flowers are green. (USDA PLANTS, 2009) Flowers are borne in axils on the old twigs. Calyx is bell-shaped and 4-9-lobed. Flowers hang on long drooping pedicels. (Peattie, 1930) Flowers bloom in clusters along the stem. (Hultman, 1978) They have no petals. (Weeks et al, 2005) Bloom color is red or green. (NPIN, 2008) Flowers are born on a shallowly lobed calyx. They are slightly asymmetric, with 7-9 lobes and ciliate margins. There are 7-9 stamens. Anthers are red and stigmas are white-ciliate and deeply divided. (FNA, 2006)
Fruit is brown. (USDA PLANTS, 2009) The samara (winged fruit) is rounded, the wing continuous all around except at the apex. Fruit may be oval or ovate, and is ciliate with fine hairs on the margins. (Peattie, 1930) Single seeds are each surrounded by a papery wing. (Hultman, 1978) Fruit is round and flat with hairy margins. The tip is deeply notched. (Weeks et al, 2005) The fruit is a yellowish to cream samara with narrow wings and hairy edges. Seeds are thick but not inflated. (UW, 2009) Samaras are yellow-cream when mature, though sometimes tinged with reddish purple (particularly in the Southern range of species). They are arrowly winged, with ciliate margins. Cilia are yellow to white. (FNA, 2006)
Leaves are green and coarse. (USDA PLANTS, 2009) Leaves are obovate-oblong and abruptly pointed. Leaves are oval, unequal-sided at the base, and sharply doubly serrate. They are rough above, dull green, and paler below. (Peattie, 1930) Elliptical with a coarsely double-toothed edge, and tapering to a point. (Hultman, 1978) Simple leaves that have a lop-sided base. Fall coloration is yellow. (Weeks et al, 2005) Dark-green leaves have variable fall color. (NPIN, 2008)
Stems This tree has a single stem growth habit. (USDA PLANTS, 2009) Erect arching branches form an umbrella-shaped crown. Twigs and buds are smooth or sparingly pubescent. (Peattie, 1930) Alternate branching is typical. Buds are elongate with chestnut-brown, slightly hairy scales. Twigs zig-zag from node to node. Lateral leaf buds lie against the twig. (Weeks et al, 2005) usually forked into many spreading branches, drooping at ends, forming a very broad, rounded, flat-topped or vaselike crown, often wider than high. (UW, 2009) Old-growth branches are smooth and not winged. Twigs are brown and pubescent to glabrous. (FNA, 2006)
Bark is flaky and gray. (Peattie, 1930) Bark is gray and tough. (Hultman, 1978) Bark is spongy until mature, and is tannish gray with thick, interlacing ridges. Inner bark is two-toned with light and dark layers. It is tan colored and spongy when young. (Weeks et al, 2005)
Tree height at 20 years is a maximum of 50' tall, at maturity 120.0' tall. (USDA PLANTS, 2009) Tree may be 50-100' tall. (Hultman, 1978) The tree was once 100'+ regularly, but is now more commonly 30-40'. (Weeks et al, 2005) It usually grows 60-80'. (NPIN, 2008)
Flowers inflorescence is less than 1" hanging cluster. (UW, 2009) Fascicles are less than 2.5 cm and the pedicel is 1-2 cm. (FNA, 2006)
Fruit is ovate and roughly 1 cm. Cilia to 1 mm. (FNA, 2006)
Leaves 4-6" long. (Hultman, 1978) Petiole is roughly 5 mm. Leaves are 7-14 × 3-7 cm. (FNA, 2006)
Range and Habitat in Illinois
American elm is common on wet flats and bottomlands but is not
restricted to these sites. In the southern bottomland regions, it
commonly occurs on terraces and flats but not in deep swamps. At higher
elevations in the Appalachians it is often limited to the vicinity of
larger streams and rarely occurs at elevations above 2,000 feet (610 m).
In the Lake States and Central States, it is found on plains and moraine
hills as well as the bottomlands and swamp margins. Along the
northeastern edge of its range, it is usually restricted to valleys
along waterways except where it has been planted on the uplands
American elm grows best on rich, well-drained loams. Growth is poor on
dry sands and where the summer water table is constantly high. In
Michigan, on loam and clay soils, growth is good when the summer water
table drops 8 to 10 feet (2.4-3.0 m) below the surface. In the South,
American elm is common on clay and silty-clay loams on bottomlands and
terraces. Growth is medium on wetter sites and good on well-drained
sites. In the arid western end of its range, American elm is restricted
to silt or clay loams in river bottoms and terraces. American elm most
commonly grows on soils of the orders Alfisols, Inceptisols, Mollisols,
and Ultisols [5,29,41].
In addition to those species mentioned in SAF Cover Types, common
associates of American elm include balsam fir (Abies balsamea), silver
maple (Acer saccharinum), sycamore (Platanus occidentalis), pin oak
(Quercus palustris), black tupelo (Nyssa sylvatica), white ash (Fraxinus
americana), sweetgum (Liquidambar styraciflua), hackberry (Celtis
occidentalis), boxelder (Acer negundo), birch (Betula spp.), and hickory
(Carya spp.) [4,19,43,50].
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: hardwood, swamp
24 Hemlock - yellow birch
25 Sugar maple - beech - yellow birch
26 Sugar maple - basswood
28 Black cherry - maple
39 Black ash - American elm - red maple
42 Bur oak
46 Eastern redcedar
52 White oak - black oak - northern red oak
53 White oak
55 Northern red oak
60 Beech - sugar maple
62 Silver maple - American elm
85 Slash pine - hardwood
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
102 Baldcypress - tupelo
103 Water tupelo - swamp tupelo
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
FRES11 Spruce - fir
FRES15 Oak - hickory
FRES16 Oak - gum - cypress
FRES17 Elm - ash - cottonwood
FRES18 Maple - beech - birch
Habitat: Plant Associations
This species is known to occur in association with the following plant community types (as classified by Küchler 1964):
K093 Great Lakes spruce - fir forest
K095 Great Lakes pine forest
K096 Northeastern spruce - fir forest
K100 Oak - hickory forest
K101 Elm - ash forest
K111 Oak - hickory - pine forest
K112 Southern mixed forest
Soils and Topography
Although American elm is common on bottom-land soils, it is found on many of the great soil groups within its range. The soils include well-drained sands, organic bogs, undifferentiated silts, poorly drained clays, prairie loams, and many intermediate combinations.
American elm grows best on rich, well-drained loams. Soil moisture greatly influences its growth. Growth is poor in droughty sands and in soils where the summer water table is high. In Michigan, on loam and clay soils, growth is good when the summer water table drops 2.4 to 3.0 in (8 to 10 ft) below the surface, medium with summer water table at 1.2 to 2.4 in (4 to 8 ft), and poor when topsoil is wet throughout the year. On sandy soils underlain with clay, growth is medium to good where the summer water table is 0.6 m (2 ft) or more below the soil surface. Organic soils are usually poor sites, but those with a summer water table at least 0.6 m (2 ft) below the surface are classed as medium sites for American elm.
In the South, American elm is common on clay and silty-clay loams on first bottoms and terraces; growth is medium on wetter sites and good on well-drained flats in first bottoms (8). In the and western end of the range, it is usually confined to the silt or clay loams in river bottoms and terraces. In shelterbelt plantings on the uplands, however, survival is generally best on sandy soils where the moisture is more evenly distributed to greater depths than in fine-textured soils. American elm most commonly grows on soils of the orders Alfisols, Inceptisols, Mollisols, and Ultisols.
Soil acidity under stands of American elm varies from acid on some of the swamp margin sites in the Lake States to mildly alkaline on the prairie soils. A soil reaction considered suitable for this species ranges from pH 5.5 to 8.0.
Leaf litter of American elm decomposes more rapidly than that of sugar maple (Acer saccharum), shagbark hickory (Carya ovata), white oak (Quercus alba), and northern red oak (Q. rubra). Under Missouri conditions, the leaves crumble readily after 18 months on the ground. They have a relatively high content of potassium and also of calcium (1 to 2 percent). Because its litter decomposes rapidly and contains many desirable nutrients, American elm is considered a "soil-improving" species.
Average annual precipitation varies from a scarce 380 min (15 in) in the Northwest to a plentiful 1520 mm (60 in) on the gulf coast. Over the central part of the species range there are about 760 to 1270 min (30 to 50 in) per year. Throughout the range most of the precipitation comes during the warm (April-September) season. Average annual snowfall generally varies from none in Florida to about 200 cm (80 in) in the Northeast. A few areas, mainly around the Great Lakes, get 254 to 380 cm (100 to 150 in) of snow per year.
The average frost-free period is about 80 to 160 days for the northern tier of States and Canada to about 200 to 320 days for the gulf coast and Southeastern States.
Flower-Visiting Insects of American Elm in Illinois
(honeybees collect pollen; this tree is wind-pollinated; all observations are from Robertson)
Apidae (Apinae): Apis mellifera cp fq
Associated Forest Cover
Black Ash-American Elm-Red Maple (Type 39) appears throughout the Northern Forest and into the Boreal Forest in Canada, and throughout the Lake States and into the northern edge of the Central Forest. In this type the most common associates, other than the type species, are as follows: In the Lake States and Canada, balsam poplar (Populus balsamifera), balsam fir (Abies balsamea), and yellow birch (Betula alleghaniensis); in Ohio and Indiana, silver maple (Acer saccharinum), swamp white oak (Quercus bicolor), sycamore (Platanus occidentalis), pin oak (Quercus palustris), black tupelo (Nyssa sylvatica), and eastern cottonwood (Populus deltoides); in New England and eastern Canada, sweet birch (Betula lenta), paper birch (B. papyrifera), gray birch (B. populifolia), silver maple, and black spruce (Picea mariana); and in New York, white ash (Fraxinus americana), slippery and rock elms (Ulmus rubra and U. thomasii), yellow birch, black tupelo, sycamore, eastern hemlock (Tsuga canadensis), bur oak (Quercus macrocarpa), swamp white oak, and silver maple.
Silver Maple-American Elm (Type 62) is common throughout the Central Forest and extends into Canada. Major associates in this type are sweetgum (Liquidambar styraciflua), pin oak, swamp white oak, eastern cottonwood, sycamore, green ash (Fraxinus pennsylvanica), and other moist site hardwoods.
Sugarberry-American Elm-Green Ash (Type 93) is found throughout the Southern Forest within the flood plains of the major rivers. Hackberry (Celtis occidentalis) replaces sugarberry (C. laevigata) in the northern part of the range. Major associates are water hickory (Carya aquatica), Nuttall (Quercus nuttallii), willow (Q. phellos), water (Q. nigra), and overcup (Q. lyrata) oak, sweetgum, and boxelder (Acer negundo).
Sycamore-Sweetgurn-American Elm (Type 94) appears as scattered stands throughout the Southern Forest region and lower Ohio River Valley. Common associates include green ash, sugarberry, hackberry, boxelder, silver maple, cottonwood, black willow (Salix nigra), water oak, and pecan (Carya illinoensis).
Wildlife uses include seed eating by granivorous birds, bird cover, bird nesting sites, and substrate for insectivorous birds. Seeds feed small mammals. It is a larval host for Mourning Cloak (Nymphalis antiopa), Columbia silkmoth (Hyalophora columbia), Question Mark (Polygonia interrogationis), Painted Lady (Vanessa cardui), and Eastern Comma (Polygonia comma). (NPIN, 2008)
Diseases and Parasites
In addition to Dutch elm disease, several other diseases also are responsible for losses in shade and forest elms. Phloem necrosis, caused by a virus (Morsus ulmi) is detected by flagging or browned leaves and butterscotch-colored phloem with a wintergreen odor. It is transmitted by the whitebanded elm leafhopper (Scaphoideus luteolus) and through root grafts. Trees usually die within a year after symptoms appear. Verticillium wilt (Verticillium albo-atrum) is soil borne and usually enters host plants through the roots. Trees show dieback symptoms similar to Dutch elm disease (10). Other diseases include diebacks caused by Cephalosporium spp. and Dothiorella ulmi; a leaf black spot (Gnomonia ulmea); twig blight (Cytosporina ludibunda); cankers (Nectria spp., Sphaeropsis ulmicola, and Phytophthora inflata); elm wetwood (Erwinia nimipressuralis); and elm mosaic virus (3,4). Some of the common wood rot fungi are Pleurotus ulmarius, P. ostreatus, Armillaria mellea, Ganoderma applanatum, Phellinus igniarius, and numerous species of Polyporus.
American elm is attacked by hundreds of insect species including defoliators, bark beetles, borers, leaf rollers, leaf miners, twig girdlers, and sucking insects. The carpenterworm (Prionoxystus robinae) bores into the sapwood and degrades the wood. Among the insects that defoliate elm are the spring cankerworm (Paleacrita vernata), the forest tent caterpillar (Malacosoma disstria), the elm leaf beetle (Pyrrhalta luteola), the whitemarked tussock moth (Orgyia leucostigma), the elm spanworm (Ennomos subsignaria), and many other leaf-eating insects that attack elm and other hardwoods. The elm cockscombgall aphid (Colopha ulmicola) forms galls on the leaves but does little damage to the tree. Several scale insects attack elm and may cause damage. Both the elm scurfy scale (Chionaspis americana) and the European elm scale (Gossyparia spuria) are widely distributed. Among the leafhoppers, the whitebanded elm leafhopper is classed as a serious pest since it is the vector for phloem necrosis (15).
Besides insect and disease losses, animal damage, and fire, climatic factors also can have an impact on survival and growth of American elm. Young forest trees may sunscald when exposed by harvesting or thinning operations. Open-grown American elm forks and develops a widespread crown that is susceptible to injury by heavy, wet snows and glaze storms. Of 37 tree species examined after an ice storm in Illinois, American elm ranked fourth in susceptibility to ice damage. In dense stands, such injuries are less severe and are not generally a management problem. Although American elm is shallow rooted in wet soils, it is fairly windfirm because the roots are widespread.
The species is reasonably drought resistant, but prolonged drought reduces growth and may cause death. During the drought of 1934, in the Midwest prairie region, losses of American elm and associated species ran as high as 80 to 90 percent. The 1951-54 drought also caused severe losses in the bottom lands of the South where American elm was more susceptible to drought than the lowland red oaks. Prolonged spring floods may cause death or growth loss. Despite suitable temperatures, in Minnesota bottom lands root elongation does not begin until the spring floods recede and soil aeration increases. On these sites and where trees are planted between street and sidewalk, buttress roots often are a result of inadequate soil aeration.
Fire damage is not a major management problem in the North; however, in southern bottom lands, fall and sometimes early spring fires are extremely damaging. Fires can kill seedling- and sapling-size trees and wound larger trees, thus admitting heartrot fungi.
Animal damage to American elm, from the sapling stage to maturity, is not a serious problem except for sapsucker injury that degrades the wood.
Number of Occurrences
Note: For many non-migratory species, occurrences are roughly equivalent to populations.
Estimated Number of Occurrences: 81 to >300
Comments: Still common, but less abundant than several decades ago.
An individual Ulmus americana was the largest street tree in Brooklyn (at 60.5 inches in diameter) and this species was the ninth most abundant street tree in Manhattan according to a 2005-2006 street tree census of New York City (available at: http://www.nycgovparks.org/sub_your_park/trees_greenstreets/images/treecount_report.pdf)
This species is included in the New York Metropolitan Flora Project of the Brooklyn Botanic Garden. Click here more information, including a distribution map for the New York metro area http://nymf.bbg.org/species/495.
This species is grown by the Greenbelt Native Plants Center on Staten Island, NY. This facility is part of the NYC Department of Parks and Recreation and its purpose is to support and promote the use of native species in planting projects. For more information, go to: http://www.nycgovparks.org/greening/greenbelt-native-plant-center.
Fire Management Considerations
Fire is usually not a major management consideration for American elm in
the North, but in the southern bottomlands, fall and early spring fires
are extremely damaging. Most fires will top-kill seedlings and saplings
and wound larger trees, providing an entry point for heart-rot fungi
Immediate Effect of Fire
American elm is easily damaged by fire . Low- and moderate-severity
fires top-kill trees up to sapling size and will wound larger trees
. In a study of the fire effects on 2- to 8-year old American elm
trees in the Missouri prairie, two spring fires of unreported severity
in March and April caused dieback of 40 and 90 percent, respectively
American elm suffered complete tissue death when the cambium was exposed
to a temperature of 140 degrees Fahrenheit (60 deg C) for 20 minutes
Tree with adventitious-bud root crown/root sucker
Secondary colonizer - on-site seed
Secondary colonizer - off-site seed
grows. When fire does occur and conditions are dry, American elm
greatly decreases following fire . Wind- and water-dispersed seed
are important in the survival of American elm following fire .
After being top-killed, young American elm will sprout from the base
following fire .
More info for the terms: climax, hardwood
Faculative Seral Species.
American elm is classed as intermediate in tolerance among eastern
hardwoods . It usually responds well to release. Once it becomes
dominant in a mixed hardwood stand, it is seldom overtaken by the other
species. It can persist for years as an intermediate but will be
replaced by tolerant hardwoods such as sugar maple (Acer saccharum) or
beech (Fagus grandifolia) if suppressed. Although American elm is not
listed as a key species in the climax types on moist sites, it is
usually one of the associated species [29,32].
Seed production and dissemination: American elm seed production may
begin as early as age 15 but is seldom abundant before age 40. When
mature, American elm is a prolific seed producer. Trees as old as 300
years have been reported to bear seed . In closed stands, seed
production is greatest in the exposed tops of trees. The winged seeds
are light and readily disseminated by the wind. Although most seeds
fall within 300 feet (90 m) of the parent tree, some may be carried 0.25
mile (0.4 km) or more. In riverbottom stands, the seeds may be carried
by the water for miles. Cleaned, unwinged seeds average 70,900 per
pound (156,000/kg) [28,46,53].
Seedling development: Germination in American elm is epigeal. Seeds
usually germinate soon after they fall, although some seeds remain
dormant until the following spring. Germination is usually 6 to 12 days
but may extend over a period of 60 days. Dormancy may be overcome by
stratification in sand for 60 days at 41 degrees Fahrenheit (5 deg C).
The seeds germinate best with night temperatures of 68 degrees
Fahrenheit (20 deg C) and day temperatures of 86 degrees Fahrenheit (30
deg C). The germination capacity averages about 65 percent
Vegetative reproduction: American elm will reproduce fairly vigorously
by stump sprouts from small trees. Large trees 150 to 250 years old
seldom sprout after cutting . Observations in undisturbed
bottomlands of Minnesota suggest that replacement of American elm may be
by root suckering .
Plant Response to Fire
The Research Paper by Bowles and others 2007 provides information on
postfire responses of several plant species, including American elm,
that was not available when this species review was originally written.
Growth Form (according to Raunkiær Life-form classification)
Reaction to Competition
Life History and Behavior
The time of flowering, seed ripening, and seed fall varies by about 100
days between the Gulf Coast and Canada. The flower buds swell early in
February in the South and as late as May in Canada. The trees are in
flower 2 to 3 weeks before the leaves unfold. The fruit ripens as the
leaves unfold or soon afterward. The seed is dispersed as it ripens and
seed fall is usually complete by the middle of March in the South and by
the middle of June in the North [3,7,29].
Samaras are wind dispersed, typically within 90 m of the tree but some can be dispersed up to 0.4 km. Waterways can carry seeds for many kilometers (Coladonato 1992).
American elm can be propagated by softwood cuttings taken in June and treated with indolebutyric acid or by leaf bud cuttings. In a test, greenhouse-grown stock rooted easier than field-grown stock. Propagation by dormant root cuttings has not been effective.
American elm seedlings can become established on moist litter, moss, and decayed logs and stumps, but do best on mineral soil. Although they do grow in full sunlight, seedlings perform best with about one-third of full sunlight during the first year. After the first year or two, they grow best in full sunlight. Seedlings that develop in saturated soils are stunted and characterized by early yellowing and loss of the cotyledons, extremely short internodes, and small leaves.
American elm can withstand flooding in the dormant season but dies if the flooding is prolonged into the growing season. Compared with other bottomland species, American elm is intermediately tolerant to complete inundation. Some may be killed by early fall frosts, but those that survive soon are hardened by temperatures alternating between 0° C (32° F) and 10° C (50° F). A constant temperature of 0° C (32° F) for 5 days also hardens the seedlings enough to avoid frost killing (7).
Studies in Iowa and southeastern Michigan on wet lowland and upland mesic sites show that despite high mortality from Dutch elm disease, the next generation will be much like the last. Although American elm has been essentially eliminated from the overstory, it is a significant part of the understory and seedling layers. Some observations suggest that there will be a shift toward more intolerant species under the dead elms. American elm may be perpetuated for generations, even though the average life span of the trees is likely to be reduced. Where seeds are available, American elm is a prominent early invader of abandoned fields. On upland sites in the Midwest, fire, as a natural component of the environment, has kept American elm from invading the prairies (1,2,12,13).
In determining vegetational patterns and succession, allelopathy is apparently not as important for species coming in under American elm as it is for species coming in under sycamore, hackberry, northern red oak, and white oak. In a test in Missouri, there was lower productivity and higher percent soil moisture under all test species but American elm. This apparently was due to toxic leaf leachate present from the four test species, but not present in leachate from American elm (11).
Seed Production and Dissemination
Adverse weather may reduce the seed crop. Spring frosts can injure and kill both flowers and fruit. Observations in Minnesota showed that while nearly ripe seeds were not injured by night temperatures of -3° C (27° F) for several successive nights, most were killed a week later when the temperature dropped to -7° C (19° F) and remained below freezing for 60 hours.
Mammals and birds also may reduce the seed crop. The flower buds, flowers, and fruit are eaten by gray squirrels. The seeds are also eaten by mice, squirrels, opossum, ruffed grouse, Northern bobwhite, and Hungarian partridge.
Flowering and Fruiting
American elm flowers are typically perfect and occur on long, slender, drooping pedicels, about 2.5 cm (1 in) long, in 3- or 4-flowered short-stalked fascicles. The anthers are bright red, the ovary and styles are light green, and the calyx is green tinged with red above the middle. With controlled pollinations, floral receptivity is greatest when stigma lobes are reflexed above the anthers. The trees are essentially self-sterile. A test in Canada showed only 1.5 percent viable seed from self-pollinated flowers. Pollination may be hampered in a wet spring since the flower anthers will not open in a saturated atmosphere (9).
Growth and Yield
Molecular Biology and Genetics
A few horticultural forms have been recognized. These are Ulmus americana columnaris, a form with a narrow columnar head, U. americana ascendens, with upright branches, and U. americana pendula, with long pendulous branches.
Hybridization within the genus Ulmus has been aimed primarily at breeding for Dutch elm disease and phloem necrosis resistance. Because of the difficulty of hybridizing American elm, which has a chromosome number twice that of all the other elms (56 versus 28), most of the breeding and selection work does not include American elm. Thousands of attempts to cross the American with the Siberian elm have failed. Reports of successful artificial hybridization and verification of hybridizing American elm with other elms are rare.
Barcode data: Ulmus americana
Statistics of barcoding coverage: Ulmus americana
Public Records: 3
Specimens with Barcodes: 5
Species With Barcodes: 1
National NatureServe Conservation Status
Rounded National Status Rank: NNR - Unranked
Rounded National Status Rank: N5 - Secure
NatureServe Conservation Status
Rounded Global Status Rank: G5 - Secure
Reasons: Widespread, still common, but far less common than several decades ago due to depletion from an exotic fungus (Dutch elm disease).
Global Short Term Trend: Decline of 30 to >90%
Comments: Declining rapidly due to Dutch elm disease, an exotic fungus transferred by bark beetles. Isolated trees less vulnerable than those in dense stands.
Comments: Highly threatened by Dutch Elm Disease (Southern Appalachian Species Viability Project 2002).
American elm has suffered greatly since the introduction of Dutch elm
disease from Europe around 1930. Since then the disease has spread over
much of the United States [46,48]. The disease is caused by the fungus
Ceratocystis ulmi. Spores of this fungus are carried by American
(Hylurgopinus rufipes) and European bark beetles (Scolytus multistria)
from diseased trees to healthy trees. The beetles breed only in dead,
dying, or recently cut elm wood and winter as larvae under the bark. In
the spring, adults emerge and fly a short distance (usually less than
500 feet [150 m]) to feed in the twig crothes or small branches in the
upper parts of the living trees. As the beetles feed, the spores are
introduced into the tree and the tree becomes diseased. After the
spores have been introduced into the tree's vascular system, the xylem
becomes plugged and a toxin is produced. The trees wilt on the small
branches and eventually on the whole limbs [16,39,47]. A program for
controlling Dutch elm disease has been described .
Most of the genetic research of elm has been concerned with the
resistance of various species, varieties, races, and hybrids to Dutch
elm disease or phloem necrosis. Natural hybridization in American elm
is uncommon, although controlled crosses have been made with Siberian
elm (Ulmus pumila). However, the success of these controlled crosses
has been quite poor [2,29]. American elm is a tetraploid, having 28
chromosomes, while most other elms have 14 chromosomes, making it
difficult to cross with other elms .
Relevance to Humans and Ecosystems
There are many studies that involve Ulmus americana, most likely due to its ubiquity and the fact that it it has been devestated by the fungal Dutch elm disease. For a review of the tree and the disease, see Hubbes 1999. It is often used in studies of stress response, for example Polanco et al. 2008 and Kozlowski and Pallardy 2002.
Hubbes M. 1999. The American elm and Dutch elm disease. The Forestry Chronicle. 75(2):265-273.
Kozlowski TT and SG Pallardy. 2002. Acclimation and adaptive responses of woody plants to environmental stresses. Botanical Review. 68(2): 270-334.
Polanco MC, JJ Zwiazek, and MC Voicu. 2008. Responses of ectomychorrhizal American elm (Ulmus americana) seedlings to salinity and soil compaction. Plant and Soil. 308(1-2):189-200.
American elm trees provide thermal cover and nesting sites for a variety
of primary and secondary cavity nesters [26,30].
Wood Products Value
The wood of American elm is coarse-grained, heavy, and strong. It lacks
durability, warps, and splits badly in seasoning . The wood is
used in the manufacture of boxes, baskets, crates, barrels, furniture,
agricultural implements, and caskets. Elm veneer is used for furniture
and decorative panels [9,51]. American elm is also used for fuel wood
Other uses and values
street ornamental in many cities in North America . The inner bark
of American elm was used in various decoctions by the Native Americans
in the southeastern United States .
Value for rehabilitation of disturbed sites
[21,38]. Its shallow and widespreading roots make it fairly windfirm
[8,56]. American elm can be propagated by cuttings, but the results
have been variable. Doran  reports that cuttings taken in June were
rooted with 94 percent success after treatment with indolebutyric acid
but rooted poorly with no treatment. The propagation of root cuttings
was ineffective for American elm in Ohio . Leafbud cuttings are
superior to soft-wood cuttings for propagating American elm .
Importance to Livestock and Wildlife
rabbits, and hares will occasionally browse the leaves and twigs
[24,49]. The seeds are eaten by a number of small birds. The
flowerbud, flower, and fruit are eaten by mice, squirrels, oppossum,
ruffed grouse, northern bobwhite, and Hungarian partridge .
The wood of American elm is moderately heavy, hard, and stiff. It has interlocked grain and is difficult to split, which is an advantage for its use as hockey sticks and where bending is needed. It is used principally for furniture, hardwood dimension, flooring, construction and mining timbers, and sheet metal work. Some elm wood goes into veneer for making boxes, crates, and baskets, and a small quantity is used for pulp and paper manufacture.
Various preparations of bark were used by pregnant women to insure stability of children, for menstrual cramps, for colds, for severe coughs, for dysentery, for "summer disease-vomiting, diarrhea and cramps," to facilitate childbirth and for parturition, for broken bones, for appendicitis, for sore eyes as an eye lotion, for gonorrhea, and for pulmonary hemorrhage. An infusion of root bark was taken for excessive menstruation. Wood was used in various capacities as a structural and vessel building material. (UM, 2009)
Ulmus americana, generally known as the American elm or, less commonly, as the white elm or water elm,[a] is a species native to eastern North America, occurring from Nova Scotia west to Alberta and Montana, and south to Florida and central Texas. The American elm is an extremely hardy tree that can withstand winter temperatures as low as −42 °C (−44 °F). Trees in areas unaffected by Dutch elm disease can live for several hundred years. A prime example of the species was the Sauble Elm, which grew beside the banks of the Sauble River in Ontario, Canada, to a height of 43 m (140 ft), with a d.b.h of 196 cm (6.43 ft) before succumbing to Dutch elm disease; when it was felled in 1968, a tree-ring count established that it had germinated in 1701.
For over 80 years, U. americana has been identified as a tetraploid, i.e. having double the usual number of chromosomes, making it unique within the genus. However, a recent study by the Agricultural Research Service of the United States Department of Agriculture has found that about 20% of wild American Elms are in fact diploid, and may even constitute another species. 
- 1 Classification
- 2 Description
- 3 Ecology
- 4 Pests and diseases
- 5 Cultivation
- 6 Other uses
- 7 Notable trees
- 8 Ulmus americana in photography
- 9 See also
- 10 Accessions
- 11 Notes
- 12 References
- 13 External links
The American elm is a deciduous hermaphroditic tree which, before the introduction of Dutch elm disease, commonly grew to > 30 m (100 ft) tall with a trunk > 1.2 m (4 ft) d.b.h supporting a high, spreading umbrella-like canopy. The leaves are alternate, 7–20 cm long, with double-serrate margins and an oblique base. The perfect flowers are small, purple-brown and, being wind-pollinated, apetalous. The flowers are also protogynous, the female parts maturing before the male, thus reducing, but not eliminating, self-fertilization, and emerge in early spring before the leaves. The fruit is a flat samara 2 cm long by 1.5 cm broad, with a circular papery wing surrounding the single 4–5 mm seed. As in the closely related European White Elm Ulmus laevis, the flowers and seeds are borne on 1–3 cm long stems. American Elm is wholly insensitive to daylight length (photoperiod), and will continue to grow well into autumn until injured by frost. Ploidy (2n = 56, or 2n = 28).
The American elm occurs naturally in an assortment of habitats, most notably rich bottomlands, floodplains, stream banks, and swampy ground, although it also often thrives on hillsides, uplands and other well-drained soils. On more elevated terrain, as in the Appalachian Mountains, it is most often found along rivers. The species' wind-dispersed seeds enable it to spread rapidly as suitable areas of habitat become available. American elm produces its seed crop in late spring (which can be as early as February and as late as June depending on the climate) and the seeds usually germinate right away with no cold stratification needed (occasionally some might remain dormant until the following year). The species attains its greatest growth potential in the northeastern US, while elms in the Deep South and Texas grow much smaller and have shorter lifespans, although conversely their survival rate in the latter regions is higher due to the climate being unfavorable for the spread of DED.
In the United States, the American elm is a major member of four major forest cover types: black ash-American elm-red maple; silver maple-American elm; sugarberry-American elm-green ash; and sycamore-sweetgum-American elm, with the first two of these types also occurring in Canada. A sugar maple-ironwood-American elm cover type occurs on some hilltops near Témiscaming, Quebec.
Pests and diseases
The American elm is highly susceptible to Dutch elm disease (DED) and elm yellows; it is also moderately preferred for feeding and reproduction by the adult elm leaf beetle Xanthogaleruca luteola, and highly preferred for feeding by the Japanese beetle Popillia japonica in the USA. Trees grown in Europe have proven very susceptible to damage by leaf-feeding insects in general, far more so than native or Asiatic elms.
U. americana is also the most susceptible of all the elms to verticillium wilt, whose external symptoms closely mimic those of DED. However, the condition is far less serious, and the tree should recover the following year.
Dutch elm disease
Dutch elm disease (DED) is a fungal disease which has ravaged the American elm, causing catastrophic die-offs in cities across the range. It has been estimated that only approximately 1 in 100,000 American elm trees is DED-tolerant, most known survivors simply having escaped exposure to the disease. However, in some areas still not populated by the Dutch elm disease-carrying elm bark beetle, the American elm continues to thrive, notably in Florida, most of Alberta and British Columbia.
The American elm is particularly susceptible to disease because the period of infection often coincides with the period, approximately 30 days, of rapid terminal growth when new springwood vessels are fully functional. Spores introduced outside of this period remain largely static within the xylem and are thus relatively ineffective.
The American elm's biology in some ways has helped to spare it from obliteration by the Dutch elm disease, in contrast to what happened to the American chestnut with the chestnut blight. The elm's seeds are largely wind-dispersed, and the tree grows quickly and begins bearing seeds at a young age. It grows well along roads or railroad tracks, and in abandoned lots and other disturbed areas, where it is highly tolerant of most stress factors. Elms have been able to survive and to reproduce in areas where the disease had eliminated old trees, although most of these young elms eventually succumb to the disease at a relatively young age. There is some reason to hope that these elms will preserve the genetic diversity of the original population, and that they eventually will hybridize with DED-resistant varieties that have been developed or that occur naturally. After 20 years of research, American scientists first developed DED-resistant strains of elms in the late 1990s.
Fungicidal injections can be administered to valuable American elms, to prevent infection. Such injections generally are effective as a preventive measure for up to three years when performed before any symptoms have appeared, but may be ineffective once the disease is evident.
In the 19th and early 20th century, American Elm was a common street and park tree due to its tolerance of urban conditions, rapid growth, and graceful form. This however led to extreme overplanting of the species, especially to form living archways over streets, which ultimately produced an unhealthy monoculture of elms that had no resistance to disease and pests. These trees' rapid growth and longevity, leading to great size within decades, also favor its horticultural use. Ohio botanist William B. Werthner, discussing the contrast between open-grown and forest-grown American elms, noted that:
In the open, with an abundance of air and light, the main trunk divides into several leading branches which leave the trunk at a sharp angle and continue to grow upward, gradually diverging, dividing and subdividing into long, flexible branchlets whose ends, at last, float lightly in the air, giving the tree a round, somewhat flattened top of beautifully regular proportions and characteristically fine twiggery.
It is this distinctive growth form that is so valued in the open-grown American elms of street plantings, lawns, and parks; along most narrower streets, elms planted on opposite sides arch and blend together into a leafy canopy over the pavement.
Introductions across the Atlantic rarely prospered, even before the outbreak of Dutch elm disease. Introduced to the UK in 1752, it was noted that the foliage of the American elm was far more susceptible to insect damage than native elms. A few, mostly young, specimens survive in British arboreta. Introduced to Australasia, the tree was listed by nurseries in Australia in the early 20th century, and is known to have been planted along the Avenue of Honour at Ballarat and the Bacchus Marsh Avenue of Honour. It is only rarely found in New Zealand.
- See the list of Elm cultivars, hybrids and hybrid cultivars for more details.
Numerous cultivars have been raised, originally for their aesthetic merit but more recently for their resistance to Dutch elm disease The total number of named cultivars is circa 45, at least 18 of which have probably been lost to cultivation as a consequence of Dutch elm disease or other factors:
- American Liberty, Ascendens, Augustine, Aurea, Beaverlodge, Beebe's Weeping, Brandon, Burgoyne, College, Columnaris, Deadfree, Delaware, Exhibition, Fiorei, Flick's Spreader, Folia Aurea Variegata, Hines, Incisa, Independence, Iowa State, Jackson, Jefferson, Kimley, Klehmii, Lake City, L'Assomption, Lewis & Clark = Prairie Expedition, Littleford, Maine, Markham, Minneapolis Park, Moline, Morden, New Harmony, Nigricans, Patmore, Pendula, Penn Treaty, Princeton, Pyramidata, Queen City, Sheyenne, Skinner Upright, Star, Valley Forge, Variegata, Vase, Washington
The National Elm Trial, begun in 2005, is currently evaluating 19 hybrid and species cultivars in scientific plantings across the United States to better assess their strengths and weaknesses.
The few disease-resistant selections made available to the public as yet include 'Valley Forge', 'New Harmony', 'Princeton', 'Jefferson', and a set of six different clones collectively known as 'American Liberty'. The United States National Arboretum released 'Valley Forge' and 'New Harmony' in late 1995, after screening tests performed in 1992–1993 showed both had unusually high levels of resistance to DED. 'Valley Forge' performed especially well in these tests. 'Princeton' has been in occasional cultivation since the 1920s, and gained renewed attention after its performance in the same screening tests showed it also to have a high degree of DED resistance. A later test performed in 2002–2003 confirmed the DED resistance of these same three varieties, and that of 'Jefferson'. 'Jefferson' was released to wholesale nurseries in 2004 and is becoming increasingly available for planting. Thus far, plantings of these four varieties generally appear to be successful.
In 2005, 90 'Princeton' elms were planted along Pennsylvania Avenue near the White House and to date are healthy and thriving. Introduced to the UK in 2001, 'Princeton' was planted by HRH The Prince of Wales to form the Anniversary Avenue from the Orchard Room reception centre to the Golden Bird statue at Highgrove House, however the trees succumbed to DED five years later and were felled and burned. In 2007, the 'Elm Recovery Project' from the University of Guelph in Ontario, Canada, reported that cuttings from healthy surviving old elms surveyed across Ontario had been grown to produce a bank of resistant trees, isolated for selective breeding of highly resistant cultivars.
Hybrids and hybrid cultivars
- Ulmus 'Rebella' (U. americana × U. parvifolia)
Thousands of attempts to cross the American elm with the Siberian elm U. pumila failed. Attempts at the Arnold Arboretum using ten other American, European and Asiatic species also ended in failure, attributed to the differences in ploidy levels, and operational dichogamy, although the ploidy factor has been discounted by other authorities.
Success was finally achieved with the autumn-flowering Chinese elm Ulmus parvifolia by the late Prof. Eugene Smalley towards the end of his career at the University of Wisconsin-Madison after he overcame the problem of keeping Chinese elm pollen alive until spring. Only one of the hybrid clones was commercially released, as 'Rebella' in 2011 by the German nursery Eisele GmbH; the clone is not available in the USA.
Other artificial hybridizations with American elm are rare, and now regarded with suspicion. Two such alleged successes by the nursery trade were 'Hamburg', and 'Kansas Hybrid', both with Siberian elm Ulmus pumila. However, given the repeated failure with the two species by research institutions, it is now believed that the "American elm" in question was more likely to have been the red elm, Ulmus rubra.
|This section requires expansion. (October 2011)|
The American Elm's wood is coarse, hard, and tough, with interlacing, contorted fibers that make it difficult to split or chop, and cause it to warp after sawing. Accordingly, the wood originally had few uses, but was found to be excellent for making hubs for wagon wheels. Later, with the advent of mechanical sawing, American elm wood was used for barrel staves, trunk-slats, and hoop-poles, and subsequently became fundamental to the manufacture of wooden automobile bodies, with the intricate fibers holding screws unusually well.
Pioneer and traditional uses
A fair number of mostly small to medium-sized American elms survive nowadays in woodlands, suburban areas, and occasionally cities, where most often the survivors had been relatively isolated from other elms and thus spared a severe exposure to the fungus. For example, in Central Park and Tompkins Square Park in New York City, stands of several large elms originally planted by Frederick Law Olmsted survive because of their isolation from neighboring areas in New York where there had been heavy mortality. The Olmsted-designed park system in Buffalo, NY  did not fare as well. A row of mature American elms graces Central Park along the entire length of Fifth Avenue from 110th St to 59th. In Akron, Ohio there is a very old elm tree that has not been infected. In historical areas of Philadelphia, Pennsylvania, there are also a few mature American elms still standing — notably in Independence Square and the Quadrangle at the University of Pennsylvania, and also at the nearby campuses of Haverford College, Swarthmore College, and The Pennsylvania State University, believed to be the largest remaining stand in the country. There are several large American Elm trees in western Massachusetts. The large Massachusetts Champion Elm stands on Summer Street in the Berkshire County town of Lanesborough, Massachusetts has been kept alive by antifungal treatments. Rutgers University has preserved 55 mature elms on and in the vicinity of Voorhees Mall on the College Avenue Campus in New Brunswick, New Jersey in addition to seven disease-resistant trees that have been planted in this area of the campus in recent years.
The largest surviving urban forest of American elms in North America is believed to be in the city of Winnipeg, Canada, where close to 200,000 elms remain. The city of Winnipeg spends $3M annually to aggressively combat the disease utilizing Dursban Turf and the Dutch Trig vaccine, losing 1500-4000 trees per year.
The USA national champion, measuring 34 m high in 2010, stands at Iberville, Louisiana. Across the Atlantic, the TROBI champion grows at Avondale in Wicklow, Ireland; last measured in 2000, it was 22.5 m high by 98 cm d.b.h..
The following are among the best-known of these huge historical American elms; for more examples, see the longer list in the article on the elm genus (Ulmus).
The Buckley Elm
Until 2001, the National Champion, standing in a field in Michigan, estimated to be as high as an 11 story building, and with a trunk 8 ft in diameter. Killed by Dutch elm disease in 2001.
The Treaty Elm (Pennsylvania)
The Treaty Elm, Philadelphia, Pennsylvania. In what is now Penn Treaty Park, the founder of Pennsylvania, William Penn, is said to have entered into a treaty of peace in 1683 with the native Lenape Turtle Clan under a picturesque elm tree immortalized in a painting by Benjamin West. West made the tree, already a local landmark, famous by incorporating it into his painting after hearing legends (of unknown veracity) about the tree being the location of the treaty. No documentary evidence exists of any treaty Penn signed beneath a particular tree. On March 6, 1810 a great storm blew the tree down. Measurements taken at the time showed it to have a circumference of 24 feet (7.3 m), and its age was estimated to be 280 years. Wood from the tree was made into furniture, canes, walking sticks and various trinkets that Philadelphians kept as relics.
The Washington Elm (Massachusetts)
The Washington Elm, Cambridge, Massachusetts. George Washington is said to have taken command of the American Continental Army under the Washington Elm in Cambridge on July 3, 1775. The tree survived until the 1920s and "was thought to be a survivor of the primeval forest". In 1872, a large branch fell from it and was used to construct a pulpit for a nearby church. The tree, an American white elm, became a celebrated attraction, with its own plaque, a fence constructed around it and a road moved in order to help preserve it. The tree was cut down (or fell — sources differ) in October 1920 after an expert determined it was dead. The city of Cambridge had plans for it to be "carefully cut up and a piece sent to each state of the country and to the District of Columbia and Alaska," according to The Harvard Crimson. As late as the early 1930s, garden shops advertised that they had cuttings of the tree for sale, although the accuracy of the claims has been doubted. A Harvard "professor of plant anatomy" examined the tree rings days after the tree was felled and pronounced it between 204 and 210 years old, making it at most 62 years old when Washington took command of the troops at Cambridge. The tree would have been a little more than two feet in diameter (at 30 inches above ground) in 1773. In 1896, an alumnus of the University of Washington, obtained a rooted cutting of the Cambridge tree and sent it to Professor Edmund Meany at the university. The cutting was planted, cuttings were then taken from it, including one planted on February 18, 1932, the 200th anniversary of the birth of George Washington, for whom Washington state is named. That tree remains on the campus of the Washington State Capitol. Just to the west of the tree is a small elm from a cutting made in 1979.
The Liberty Tree (Massachusetts)
- The Liberty Tree, an elm on Boston Common in Boston, Massachusetts, was a rallying point for the growing resistance to the rule of England over the American colonies..
George Washington's Elm (District of Columbia)
- George Washington's Elm, Washington, D.C. George Washington supposedly had a favorite spot under an elm tree near the United States Capitol Building from which he would watch construction of the building. The elm stood near the Senate wing of the Capitol building until 1948.
The Logan Elm (Ohio)
The Logan Elm that stood near Circleville, Ohio, was one of the largest American elms anywhere. The 65-foot-tall (20 m) tree had a trunk circumference of 24 feet (7.3 m) and a crown spread of 180 feet (55 m). Weakened by Dutch elm disease, the tree died in 1964 from storm damage. The Logan Elm State Memorial commemorates the site and preserves various associated markers and monuments. According to tradition, Chief Logan of the Mingo tribe delivered a passionate speech at a peace-treaty meeting under this elm in 1774,
Another notable American elm, named Herbie, was the tallest American elm in New England until it was cut down on January 19, 2010, after Dutch elm disease became fatal. Herbie was 110 feet (34 m) tall at its peak and had a circumference of 20.3 feet (6.2 m), or a diameter of approximately 6.5 feet (2.0 m). The tree stood in Yarmouth, Maine, where it was cared for by the town's tree warden, Frank Knight.
When cut down, Herbie was 217 years old. Herbie's wood is of interest to dendroclimatologists, who will use cross-sections of the trunk to help answer questions about climate during the tree's lifetime.
The Survivor Tree
An American elm, located in a parking lot directly across the street from the Alfred P. Murrah Federal Building in Oklahoma City, OK, survived a terrorist bombing on April 19, 1995 that killed 168 people and destroyed the building. Damaged in the blast, with fragments lodged in its trunk and branches, it was nearly cut down in efforts to recover evidence. However, nearly a year later the tree began to bloom. It is now an important part of the Oklahoma City National Memorial, and the Survivor Tree is featured prominently on the official logo of the memorial.
Ulmus americana in photography
The nobility and arching grace of the American elm in its heyday, on farms, in villages, in towns and on campuses, were celebrated in the books of photographs of Wallace Nutting (Massachusetts Beautiful, N.Y. 1923, and other volumes in the series) and of Samuel Chamberlain (The New England Image, New York, 1962).
- North America
- Arnold Arboretum, acc. nos. 250-53 (cult. material), 412-86 wild collected in the USA.
- Bernheim Arboretum and Research Forest, Clermont, Kentucky. No details available.
- Denver Botanic Gardens, one specimen, no details.
- Latina Nursery, Searcy, AR, two specimens, no details.
- Holden Arboretum, acc. nos. 2005-17, 65-632, 80-663, all of unrecorded provenance.
- Longwood Gardens, acc. nos. 1997-0074, L-0352, sources unrecorded.
- Missouri Botanical Garden, St. Louis, Missouri. acc. nos. 1969-6172, 1986-0206, 1986-0207, 1986-0208.
- New York Botanical Garden, acc. nos. 877/97, 944/96, 1854/99, 2111/99, 06791, all unrecorded provenance.
- Phipps Conservatory & Botanical Gardens, acc. nos. 00/1265, 99/0660.
- Scott Arboretum, acc. no. S000339, no other details available.
- U S National Arboretum, Washington, D.C., USA. Acc. nos. 64254, 64255, 64256, 66355, 66426, 68988, 69304, 66341.
- Brighton & Hove City Council, UK. NCCPG elm collection.
- Dubrava Arboretum, Lithuania. No accession details available.
- Hortus Botanicus Nationalis, Salaspils, Latvia. Acc. nos. 18087,88,89,90,91,92.
- Wakehurst Place Garden, Wakehurst Place, UK. Acc. nos. 1994-67, 1994-68, 1991-1163.
- Linnaean Gardens of Uppsala, Sweden. Acc. nos. 1976-2713,0000-2170
- Strona Arboretum, University of Life Sciences, Warsaw, Poland. No accession details available.
- Royal Botanic Garden Edinburgh, UK. Acc. no. 19901741, wild collected in Canada
- Tallinn Botanic Garden, Estonia. No accession details available.
- Thenford House arboretum, Northamptonshire, UK. No accession details available.
- University of Copenhagen, Botanic Garden. Acc. no. P1971-5201, wild collected in the USA.
- The name "water elm" is also used for Planera aquatica, another species in the Ulmaceae.
- "Ulmus americana". NatureServe Explorer. NatureServe. Retrieved 2007-07-06.
- "Of Elms and Orioles". Emmitsburg News-Journal: The New Forest Society. Retrieved December 15, 2014.
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- Hans, A. S. (1981). "Compatibility and Crossability Studies in Ulmus". Silvae Genetica 30: 4–5.
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- Werthner, William B. (1935). Some American Trees: An Intimate Study of Native Ohio Trees. New York: The Macmillan Company. pp. xviii, 398.
- Strausbaugh, P.D.; Core, E.L. (1978). Flora of West Virginia (2 ed.). Morgantown, WV: Seneca Books, Inc. pp. xl, 1079.
- "American Elm". United States Forest Service. Retrieved December 14, 2014.
- Brown, Jean-Louis (1981). Les forêts du Témiscamingue, Québec: écologie et photo-interprétation (in French). Quebec City, Canada: Laboratoire d'écologie forestière, Université Laval, Québec. ISBN 978-2-9201-0404-4.
- Miller, F.; Ware, G. (2001). "Resistance of Temperate Chinese Elms (Ulmuss spp.) to Feeding of the Adult Elm Leaf Beetle (Coleoptera: Chrysomelidae)". Journal of Economic Entomology 94 (1): 162–166. doi:10.1603/0022-0493-94.1.162.
- Miller, F.; Ware, G.; Jackson, J. (2001). "Preference of Temperate Chinese Elms (Ulmuss spp.) for the Feeding of the Japanese Beetle (Coleoptera: Scarabaeidae)". Journal of Economic Entomology 94 (2): 445–448. doi:10.1603/0022-0493-94.2.445.
- Elwes, H. J.; Henry, A. (1913). The Trees of Great Britain & Ireland (PDF) VII. pp. 1848–1929. Republished 2004, Cambridge University Press, ISBN 9781108069380
- Pegg, G. F.; Brady, B. L. (2002). Verticillium Wilts. Wallingford, Oxfordshire, UK: CABI Publishing. ISBN 0-85199-529-2.
- "New American Elms Restore Stately Trees". Agricultural Research Service, United States Department of Agriculture. July 1996. Retrieved December 18, 2014.
- Smalley, E. G. (1963). "Seasonal Fluctuations in Susceptibility of Young Elm Seedlings to Dutch Elm Disease". Phytopathology 53 (7): 846–853.
- Stennes, Mark (2003). "Good News for the American Elm". Shade Tree Advocate 5 (4): 6.
- Journal (Auckland Botanical Society) 58 (1). June 2003. Missing or empty
- Townsend, A. M.; Bentz, S. E.; Douglass, L. W. (March 2005). "Evaluation of 19 American Elm Clones for Tolerance to Dutch Elm Disease" (PDF). Journal of Environmental Horticulture: 21–24.
- Costello, L. R. (March 2004). "A 10-year Evaluation of the Performance of Four Elm Cultivars in California, U. S.". Journal of Arboriculture.
- Elm Recovery Project, University of Guelph
- "Scientists Breed Supertrees to Beat Dutch Elm". Canada.com. September 11, 2007. Retrieved December 21, 2014.
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- Heybroek, H. M.; Goudzwaard, L.; Kaljee, H. (2009). Iep of olm, karakterboom van de Lage Landen (Elm, A Tree With Character of the Low Countries (in Dutch). Zeist, Netherlands: KNNV Uitgeverij. ISBN 978-9-0501-1281-9.
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- Manas, Steve (May 8, 2008). "Voorhees Mall Elms Add to Commencement's Ambience". Rutgers University. Retrieved December 24, 2014.
- "Elm Bark Beetle Control Program" (PDF). City of Winnipeg. August 7, 2009. Retrieved December 24, 2014.
- Rumbolt, Colin (November 17, 2009). "Dutch Elm Vaccine Tested In Winnipeg". The Manitoban. Retrieved December 24, 2014.
- "The 2012 National Register of Big Trees" (PDF). American Forests. 2012. Retrieved December 24, 2012.
- Robbins, J. (2013). The Man Who Plants Trees. London: Profile Books. ISBN 978-1781250624.
- "Penn Treaty Elm". Haverford College Arboretum. Retrieved December 28, 2014.
- Platt, Rutherford (1992). 1001 Questions Answered About Trees. Courier Dover Publications. p. 19. ISBN 0-486-27038-6.
- Jacobson, Arthur Lee. "Arthur Lee Jacobson: Trees of the Washington State Capitol Campus".
- "Big Day for Curio Hunter When Famous Elm is Cut". The Harvard Crimson. Harvard University. October 23, 1920. Retrieved December 24, 2014.
- Jack, J. G. (December 10, 1931). "The Cambridge Washington Elm" (PDF). Bulletin of Popular Information. Arnold Arboretum, Harvard University. Retrieved December 24, 2014.
- Kessler, Ronald (October 3, 2011). "America Must Remember Boston’s Liberty Tree". Newsmax. Retrieved December 27, 2014.
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- "The Roots of Tragedy". Ohio Magazine. Retrieved December 14, 2014.
- Sharp, David (January 31, 2010). "Do Rings of Herbie the Elm Have Age, Climate Data?". Boston.com. Associated Press. Retrieved December 24, 2014.
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The Florida Elm (U. americana var. floridana) is smaller than the type, and occurs naturally in north and central Florida south to Lake Okeechobee, growing to a maximum height of 22 m, with a slightly greater spread 
Ulmus americana is the state tree for Massachusetts and for North Dakota.
The American elm is susceptible to numerous diseases, including Dutch elm disease. Ulmus americana has been a street and shade tree of choice because of its fast growth and pleasant shape and size. The species still exists in substantial numbers both as shade trees and in nature.
Numerous infraspecific taxa have been recognized in Ulmus americana (A. J. Rehder 1949; P. S. Green 1964).
Native American tribes frequently used parts of Ulmus americana for a variety of medicinal purposes, including treatment of coughs and colds, sore eyes, dysentary, diarrhea, broken bones, gonorrhea, and pulmonary hemorrhage, as a gynecological aid, as a bath for appendicitis, and as a wash for gunwounds (D. E. Moerman 1986).
Names and Taxonomy
americana L. . Recognized varieties include U. americana var.
americana and U. americana var. floridana, which is restricted to the
coastal plains from eastern North Carolina to central Florida [15,27].
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