Gnetophyta
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{{Taxobox
| name = Gnetophyta
| image = Welwitchia.jpg
| image_width = 240px
| image_caption = ''[[Welwitschia mirabilis]]''
| regnum = [[Plant]]ae
| divisio = '''Gnetophyta'''
| classis = '''Gnetopsida'''
| subdivision_ranks = Genera
| subdivision =
*''[[Gnetum]]''
*''[[Welwitschia]]''
*''[[Ephedra (genus)|Ephedra]]''
}}
The [[plant]] division '''Gnetophyta''' or gnetophytes comprise three related families of [[woody plant]]s grouped in the [[gymnosperm]]s. The gnetophytes differ from other gymnosperms in having [[vessel element]]s as in the [[flowering plant]]s ('''Angiosperms''' or '''Magnoliophytes''').
The living Gnetophyta comprise three genera:
*''[[Gnetum]]''
*''[[Welwitschia]]''
*''[[Ephedra (genus)|Ephedra]]''
''[[Gnetum]]'' species are mostly [[wood]]y [[Vine|climbers]] in tropical forests. However, the most well-known member of this group, ''[[Gnetum gnemon]]'', is a tree. Its seeds are used to produce a crispy ''[[krupuk]]'' snack known as ''emping'' or ''krupuk belinjo''.
''[[Welwitschia]]'' comprises only one species, ''Welwitschia mirabilis''. It grows only in the deserts of [[Namibia]] and [[Angola]]. The plant is strange in having only two large strap-like leaves for all its life. These grow continuously from the base, and are usually tattered at the ends by flapping in the winds.
Plants of the genus ''[[Ephedra (genus)|Ephedra]]'' are known as jointfirs because they have long slender branches which bear tiny scale-like leaves at their nodes. ''Ephedra'' has been traditionally used as a [[stimulant]], but is a [[controlled substance]] today in many juristictions because of the risk of harmful or even fatal [[overdose|overdosing]].
In some classifications all three genera are placed in a single order (Gnetales) but in others distributed among three orders, each containing a single family and genus.
''Gnetum'' and ''Welwitschia'' diverged from each other more recently than from ''Ephedra''.<ref name="crane">{{cite journal | url = http://www.amjbot.org/cgi/content/full/91/10/1683 | title = Fossils and plant phylogeny | author = Peter R. Crane, Patrick Herendeen and Else Marie Friis | journal = American Journal of Botany | year = 2004 | volume = 91 | pages = 1683–1699 | doi = 10.3732/ajb.91.10.1683 }}</ref>
Knowledge of fossils of the gnetophytes has increased greatly since the 1980s.<ref name="crane"/> There are fossils from the [[Permian]],<ref>{{cite journal | url = http://aob.oxfordjournals.org/cgi/content/full/94/2/281 | title = A New Permian Gnetalean Cone as Fossil Evidence for Supporting Current Molecular Phylogeny | author = Zi-Qiang Wang | journal = Annals of Botany | year = 2004 | volume = 94 | issue = 2 | pages = 281–288 | doi = 10.1093/aob/mch138 | pmid = 15229124 }}</ref> the [[Triassic]], and the [[Jurassic]] which may belong to the gnetophytes, but this is uncertain.<ref name="rydin">{{cite journal | url = http://aob.oxfordjournals.org/cgi/content/full/98/1/123 | journal = Annals of Botany | year = 2006 | volume = 98 | issue = 1 | pages = 123–140 | doi = 10.1093/aob/mcl078 | title = Former Diversity of Ephedra (Gnetales): Evidence from Early Cretaceous Seeds from Portugal and North America | author = Catarina Rydin, Kaj Raunsgaard Pedersen, Peter R. Crane and Else Marie Friis | pmid = 16675607}}</ref> The fossil record is richer starting in the early [[Cretaceous]], with fossils of plants as well as [[seed]]s and [[pollen]] which can be clearly assigned to the gnetophytes.<ref name="rydin"/>
Molecular phylogenies of extant gymnosperms have conflicted with morphological characters with regard to whether the gymnosperms as a whole (including gnetophytes) comprise a [[monophyletic group]] or a [[paraphyletic]] one that gave rise to angiosperms. At issue is whether the Gnetophyta are the [[sister group]] of [[angiosperms]], or whether they are sister to, or nested within, other extant gymnosperms. Numerous fossil gymnosperm clades once existed that are morphologically at least as distinctive as the four living [[gymnosperm]] groups, such as [[Bennettitales]], ''Caytonia'' and the glossopterids. When these gymnosperm fossils are considered the question of gnetophyte relationships to other seed plants becomes even more complicated.
== References ==
<references/>
*Burleigh, J. G., and S. Mathews. 2004. Phylogenetic signal in nucleotide data from seed plants: implications for resolving the seed plant tree of life. ''American Journal of Botany'' 91: 1599-1613 ([http://www.amjbot.org/cgi/content/abstract/91/10/1599 abstract])
*Gifford, Ernest M., Adriance S. Foster. 1989. Morphology and Evolution of Vascular Plants. Third edition. WH Freeman and Company, New York.
*Hilton, Jason, and Richard M. Bateman. 2006. Pteridosperms are the backbone of seed-plant phylogeny. ''Journal of the Torrey Botanical Society'' 133: 119-168 ([http://www.bioone.org/perlserv/?request=get-abstract&doi=10.3159%2F1095-5674(2006)133%5B119%3APATBOS%5D2.0.CO%3B2&ct=1 abstract])
[[Category:Gnetophyta| ]]
[[ar:شعبة الجنتويات]]
[[bg:Гнетови]]
[[da:Gnetophyta]]
[[de:Gnetopsida]]
[[es:Gnetophyta]]
[[fr:Gnetales]]
[[it:Gnetophyta]]
[[he:גנטאים]]
[[lt:Gnetūnai]]
[[hu:Leplesmagvúak]]
[[ja:グネツム綱]]
[[pl:Gniotowe]]
[[pt:Gnetófita]]
[[ro:Gnetatae]]
[[ru:Гнетовые]]
[[sk:Lianovcorasty]]
[[fi:Gnetophytina]]
[[sv:Gnetophyta]]
[[vi:Ngành Dây gắm]]
[[to:ʻakau sukau]]
[[uk:Гнетоподібні]]
[[zh:买麻藤纲]]