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Vascular Plants

Tracheophyta

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Pteridophytes are the division of plants that include the ferns and so-called fern allies. This is an extremely diverse group of approximately 12,000 species of plants, so divergent that in some classifications, they have been placed in four divisions (e.g., Cronquist et al. 1966). However, three common features unite the group: 1) They are not flowering plants, but instead produce and are dispersed by spores, rather than seeds; 2) They feature a complicated life cycle that includes an alternative of generations, with germination of spores into a gametophyte generation, which is haploid (containing half the normal chromosome number, n) and usually short-lived and inconspicuous and cannot themselves produce spores, but are essential to the reproductive cycle and that exists in a separate stage from the spore-producing plants, sporophytes, which are usually perennial and conspicuous, and have roots, stems (often rhizomatous), and leaves, and are diploid, with 2n chromosomes. 3) They require free (standing) water in order to reproduce, because their flagellate sperm swim to fertilize the eggs; for this reason, many of the species live in moist habitats. In addition to sexual reproduction through the alternation of generations, many pteridophytes reproduce extensively through vegetative (clonal) propagation, typically from rhizomatous stems, but also from leaves and roots. Because of this, sterile hybrid forms that arise may persist and become common in local regions. In all but a couple of genera, modern pteridophytes lack secondary growth, including cambium tissue (which produces cork cells and bark on trees). Their characteristics remain similar those found in many of the earliest land plants. However, in contrast to mosses (Bryophyta), they are vascular plants, containing vessels (xylem and phloem) to transport water and nutrients through the stem tissues. Although no single fern species is of widespread economic importance, over 700 species from 124 genera are grown as ornamentals, either indoors or outdoors for landscaping, and some species are increasingly used in North Amerian gardens where browsing by white-tailed deer (Odocoileus virginiana) is a problem. (Ferns in general are less likely to be browsed by deer than grasses and flowering species, but cultivars of fern species including Athyrium, Dryopteris, and Osmunda are particularly promoted as deer resistant.) Ferns are also sometimes used as a food plant--the emerging stems of some species are gathered in the wild and eaten as a vegetable (fiddlehead ferns, actually the unfurling leaves of various fern species, including Pteridium aquilinum (bracken fern), Matteuccia struthiopteris (ostrich fern), Osmunda cinnamomea (cinnamon fern or buckhorn fern), Osmunda regalis (royal fern), and Athyrium esculentum (vegetable fern), although some of these species are reported to contain potential carcinogens. Many fern species also have traditional medicinal uses. (Cronquist et al. 1966, Hoshizaki and Moran 2001, Moran 2004, Wagner and Smith 1993, Wikipedia 2012.)
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Brief Summary

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The vascular plants (or tracheophytes) are characterized by the presence of vascular tissue (xylem and phloem) for structural support and for long-distance movement of water and nutrients throughout the plant body.

The relationships among the major groups of vascular plants have become clearer in recent years. Investigations into the origin and evolution of the major groups of vascular plants indicate that there is a deep division of the vascular plants into two lineages. One of these lineages includes only the lycophytes (clubmosses, spikemosses, and quillworts), accounting for less than 1% of vascular plant species. The other lineage (known as Euphyllophyta) includes two major clades: the spermatophytes or seed plants (including more than 250,000 species of angiosperms [flowering plants], conifers, cycads, gnetophytes, and the Gingko) and the monilophytes or ferns (sensu lato, including the horsetails, whisk ferns, and eusporangiate and leptosporangiate ferns, with most of the roughly 12,000 monilophyte species being leptosporangiate ferns).

(Pryer et al. 2001; Pryer et al. 2004; Smith et al. 2006; Lehtonen 2011 and references therein)

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The horsetails or scouring rushes (Equisetophyta, Sphenophyta, Arthrophyta, and Equisetaceae are among the names that have been used for this group) are now believed to form a monophyletic group with the ferns that is known as the "monilophytes" (although the position of the horsetails within the monilophytes is not yet fully resolved, they may be nested among other ferns);this clade, in turn, is the sister group to the seed plants (Pryer et al. 2001; Schneider et al. 2009 and references therein; Rai and Graham 2010 and references therein). There is just one extant genus, Equisetum, which includes around 15 extant species. Equisetum is nearly cosmopolitan (not native to Australia and New Zealand, but they are exotic weeds there). Many Equisetum have a high silica content and can be used to scour pots (explaining the name "scouring rush"). Horsetails have an extensive and diverse fossil record and several hundred million years ago widespread tree-sized relatives reached 30 m in height (even today, some Equisetum species can reach an impressive size--although nothing approaching 30 m!).

(Mabberley 2008)

For more information on the biology of horsetails, see Husby (2013) and Chad Husby's website.

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Brief Summary

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The relationship of "pteridophytes" to other vascular plants (= tracheophytes) has become clearer in recent years. Investigations into the origin and evolution of the major groups of vascular plants indicate that there is a deep division of the vascular plants into two lineages. One of these lineages includes only the lycophytes (clubmosses, spikemosses, and quillworts). The other lineage includes two major clades: the spermatophytes or seed plants (including more than 250,000 species of angiosperms [flowering plants], conifers, cycads, gnetophytes, and the Gingko) and the monilophytes or ferns (sensu lato, including the horsetails, whisk ferns, and eusporangiate and leptosporangiate ferns, with most of the roughly 12,000 monilophyte species being leptosporangiate ferns). The spermatophytes and monilophytes together comprise a clade known as Euphyllophyta.

Plants in the lycophyte and monilophyte clades are apparently not each other's closest relatives (since the monilophytes are believed to be sister to the seed plants), but because they both produce spores and not seeds, the lycophytes and ferns have traditionally been grouped together in what is now generally recognized to be a paraphyletic group referred to as "pteridophytes" or "ferns and fern allies".

(Pryer et al. 2001; Pryer et al. 2004; Smith et al. 2006; Lehtonen 2011 and references therein)

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Vascular plant

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Vascular plants (from Latin vasculum: duct), also known as tracheophytes (from the equivalent Greek term trachea), form a large group of plants (c. 308,312 accepted known species[5]) that are defined as land plants that have lignified tissues (the xylem) for conducting water and minerals throughout the plant. They also have a specialized non-lignified tissue (the phloem) to conduct products of photosynthesis. Vascular plants include the clubmosses, horsetails, ferns, gymnosperms (including conifers) and angiosperms (flowering plants). Scientific names for the group include Tracheophyta,[6][2]:251 Tracheobionta[7] and Equisetopsida sensu lato. Some early land plants (the rhyniophytes) had less developed vascular tissue; the term eutracheophyte has been used for all other vascular plants.

Characteristics

Botanists define vascular plants by three primary characteristics:

  1. Vascular plants have vascular tissues which distribute resources through the plant. Two kinds of vascular tissue occur in plants: xylem and phloem. Phloem and xylem are closely associated with one another and are typically located immediately adjacent to each other in the plant. The combination of one xylem and one phloem strand adjacent to each other is known as a vascular bundle.[8] The evolution of vascular tissue in plants allowed them to evolve to larger sizes than non-vascular plants, which lack these specialized conducting tissues and are thereby restricted to relatively small sizes.
  2. In vascular plants, the principal generation phase is the sporophyte, which produces spores and is diploid (having two sets of chromosomes per cell). (By contrast, the principal generation phase in non-vascular plants is the gametophyte, which produces gametes and is haploid - with one set of chromosomes per cell.)
  3. Vascular plants have true roots, leaves, and stems, even if some groups have secondarily lost one or more of these traits.

Cavalier-Smith (1998) treated the Tracheophyta as a phylum or botanical division encompassing two of these characteristics defined by the Latin phrase "facies diploida xylem et phloem instructa" (diploid phase with xylem and phloem).[2]:251

One possible mechanism for the presumed evolution from emphasis on haploid generation to emphasis on diploid generation is the greater efficiency in spore dispersal with more complex diploid structures. Elaboration of the spore stalk enabled the production of more spores and the development of the ability to release them higher and to broadcast them farther. Such developments may include more photosynthetic area for the spore-bearing structure, the ability to grow independent roots, woody structure for support, and more branching.

Phylogeny

A proposed phylogeny of the vascular plants after Kenrick and Crane 1997[9] is as follows, with modification to the gymnosperms from Christenhusz et al. (2011a),[10] Pteridophyta from Smith et al.[11] and lycophytes and ferns by Christenhusz et al. (2011b) [12] The cladogram distinguishes the rhyniophytes from the "true" tracheophytes, the eutracheophytes.[9]

PolysporangiatesTracheophytes Eutracheophytes Euphyllophytina Lignophytes Spermatophytes

Pteridospermatophyta † (seed ferns)

   

Cycadophyta (cycads)

   

Pinophyta (conifers)

   

Ginkgophyta (ginkgo)

   

Gnetophyta

   

Magnoliophyta (flowering plants)

     

Progymnospermophyta

    Pteridophyta    

Pteridopsida (true ferns)

   

Marattiopsida

   

Equisetopsida (horsetails)

   

Psilotopsida (whisk ferns & adders'-tongues)

   

Cladoxylopsida

        Lycophytina  

Lycopodiophyta

   

Zosterophyllophyta

       

Rhyniophyta

       

Aglaophyton

   

Horneophytopsida

   

This phylogeny is supported by several molecular studies.[11][13][14] Other researchers state that taking fossils into account leads to different conclusions, for example that the ferns (Pteridophyta) are not monophyletic.[15]

Nutrient distribution

"
Photographs showing xylem elements in the shoot of a fig tree (Ficus alba): crushed in hydrochloric acid, between slides and cover slips.

Water and nutrients in the form of inorganic solutes are drawn up from the soil by the roots and transported throughout the plant by the xylem. Organic compounds such as sucrose produced by photosynthesis in leaves are distributed by the phloem sieve tube elements.

The xylem consists of vessels in flowering plants and tracheids in other vascular plants, which are dead hard-walled hollow cells arranged to form files of tubes that function in water transport. A tracheid cell wall usually contains the polymer lignin. The phloem however consists of living cells called sieve-tube members. Between the sieve-tube members are sieve plates, which have pores to allow molecules to pass through. Sieve-tube members lack such organs as nuclei or ribosomes, but cells next to them, the companion cells, function to keep the sieve-tube members alive.

Transpiration

The most abundant compound in all plants, as in all cellular organisms, is water which serves an important structural role and a vital role in plant metabolism. Transpiration is the main process of water movement within plant tissues. Water is constantly transpired from the plant through its stomata to the atmosphere and replaced by soil water taken up by the roots. The movement of water out of the leaf stomata creates a transpiration pull or tension in the water column in the xylem vessels or tracheids. The pull is the result of water surface tension within the cell walls of the mesophyll cells, from the surfaces of which evaporation takes place when the stomata are open. Hydrogen bonds exist between water molecules, causing them to line up; as the molecules at the top of the plant evaporate, each pulls the next one up to replace it, which in turn pulls on the next one in line. The draw of water upwards may be entirely passive and can be assisted by the movement of water into the roots via osmosis. Consequently, transpiration requires very little energy to be used by the plant. Transpiration assists the plant in absorbing nutrients from the soil as soluble salts.

Absorption

Living root cells passively absorb water in the absence of transpiration pull via osmosis creating root pressure. It is possible for there to be no evapotranspiration and therefore no pull of water towards the shoots and leaves. This is usually due to high temperatures, high humidity, darkness or drought.

Conduction

Xylem and phloem tissues are involved in the conduction processes within plants. Sugars are conducted throughout the plant in the phloem, water and other nutrients through the xylem. Conduction occurs from a source to a sink for each separate nutrient. Sugars are produced in the leaves (a source) by photosynthesis and transported to the growing shoots and roots (sinks) for use in growth, cellular respiration or storage. Minerals are absorbed in the roots (a source) and transported to the shoots to allow cell division and growth.[16]

See also

References

  1. ^ Sinnott, E. W. 1935. Botany. Principles and Problems, 3d edition. McGraw-Hill, New York.
  2. ^ a b c Cavalier-Smith, T. (1998), "A revised six-kingdom system of life" (PDF), Biological Reviews of the Cambridge Philosophical Society, 73 (3): 203–266, doi:10.1111/j.1469-185X.1998.tb00030.x
  3. ^ D. Edwards; Feehan, J. (1980). "Records of Cooksonia-type sporangia from late Wenlock strata in Ireland". Nature. 287 (5777): 41–42. doi:10.1038/287041a0.
  4. ^ Parfrey, Laura Wegener; Lahr, Daniel J. G.; Knoll, Andrew H.; Katz, Laura A. (August 16, 2011). "Estimating the timing of early eukaryotic diversification with multigene molecular clocks". Proceedings of the National Academy of Sciences of the United States of America. 108 (33): 13624–13629. doi:10.1073/pnas.1110633108. PMC 3158185. PMID 21810989.
  5. ^ Christenhusz, M. J. M. & Byng, J. W. (2016). "The number of known plants species in the world and its annual increase". Phytotaxa. 261 (3): 201–217. doi:10.11646/phytotaxa.261.3.1.
  6. ^ Abercrombie, Hickman & Johnson. 1966. A Dictionary of Biology. (Penguin Books)
  7. ^ "ITIS Standard Report Page: Tracheobionta". Retrieved September 20, 2013.
  8. ^ https://basicbiology.net/plants/physiology/xylem-phloem
  9. ^ a b Kenrick, Paul; Crane, Peter R. (1997). The Origin and Early Diversification of Land Plants: A Cladistic Study. Washington, D.C.: Smithsonian Institution Press. ISBN 1-56098-730-8.
  10. ^ Christenhusz, Maarten J. M.; Reveal, James L.; Farjon, Aljos; Gardner, Martin F.; Mill, R.R.; Chase, Mark W. (2011). "A new classification and linear sequence of extant gymnosperms" (PDF). Phytotaxa. 19: 55–70. doi:10.11646/phytotaxa.19.1.3.
  11. ^ a b Smith, Alan R.; Pryer, Kathleen M.; Schuettpelz, E.; Korall, P.; Schneider, H.; Wolf, Paul G. (2006). "A classification for extant ferns" (PDF). Taxon. 55 (3): 705–731. doi:10.2307/25065646. JSTOR 25065646.
  12. ^ Christenhusz, Maarten J. M.; Zhang, Xian-Chun; Schneider, Harald (2011). "A linear sequence of extant families and genera of lycophytes and ferns" (PDF). Phytotaxa. 19: 7–54. doi:10.11646/phytotaxa.19.1.2.
  13. ^ Pryer, K. M.; Schneider, H.; Smith, AR; Cranfill, R; Wolf, PG; Hunt, JS; Sipes, SD (2001). "Horsetails and ferns are a monophyletic group and the closest living relatives to seed plants". Nature. 409 (6820): 618–22. doi:10.1038/35054555. PMID 11214320.
  14. ^ Pryer, K. M.; Schuettpelz, E.; Wolf, P. G.; Schneider, H.; Smith, A. R.; Cranfill, R. (2004). "Phylogeny and evolution of ferns (monilophytes) with a focus on the early leptosporangiate divergences". American Journal of Botany. 91 (10): 1582–1598. doi:10.3732/ajb.91.10.1582. PMID 21652310.
  15. ^ Rothwell, G.W. & Nixon, K.C. (2006). "How Does the Inclusion of Fossil Data Change Our Conclusions about the Phylogenetic History of Euphyllophytes?". International Journal of Plant Sciences. 167 (3): 737–749. doi:10.1086/503298.
  16. ^ Chapters 5, 6 and 10 Taiz and Zeiger Plant Physiology 3rd Edition SINAUER 2002
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Vascular plant: Brief Summary

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Vascular plants (from Latin vasculum: duct), also known as tracheophytes (from the equivalent Greek term trachea), form a large group of plants (c. 308,312 accepted known species) that are defined as land plants that have lignified tissues (the xylem) for conducting water and minerals throughout the plant. They also have a specialized non-lignified tissue (the phloem) to conduct products of photosynthesis. Vascular plants include the clubmosses, horsetails, ferns, gymnosperms (including conifers) and angiosperms (flowering plants). Scientific names for the group include Tracheophyta,:251 Tracheobionta and Equisetopsida sensu lato. Some early land plants (the rhyniophytes) had less developed vascular tissue; the term eutracheophyte has been used for all other vascular plants.

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