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Gnetophyta
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==Ecology and morphology== Unlike most biological groupings, it is difficult to find many common characteristics between all of the members of the gnetophytes.<ref name="Arber and Parkin">{{cite journal | title = Studies on the evolution of the angiosperms: the relationship of the angiosperms to the Gnetales |author1=Arber, E.A.N. |author2=Parkin, J. | journal = Annals of Botany | year = 1908 | volume = 22 | issue = 3 | pages = 489β515 | doi = 10.1093/oxfordjournals.aob.a089185 }}</ref> The two [[synapomorphy|common characteristics]] most commonly used are the presence of enveloping [[bract]]s around both the [[ovule]]s and [[microsporangia]] as well as a micropylar projection of the outer membrane of the ovule that produces a [[pollination]] droplet,<ref name="Judd">Judd, W.S.; Campbell, C.S.; Kellogg, E.A.; Stevens, P.F.; and Donoghue, M.J. (2008) Plant Systematics: A Phylogenetics Approach. 3rd ed. Sunderland, Massachusetts, USA: Sinauer Associates, Inc.</ref> though these are highly specific compared to the similarities between most other plant divisions. L. M. Bowe refers to the gnetophyte genera as a "bizarre and enigmatic" trio<ref name="Bowe">{{cite journal | title = Phylogeny of seed plants based on all three genomic compartments: Extant gymnosperms are monophyletic and Gnetales' closest relatives are conifers |author1=Bowe, L.M. |author2=Coat, G. |author3=dePamphilis, C.W. | journal = Proceedings of the National Academy of Sciences | year = 2000 | volume = 97 | pages = 4092β4097 | doi = 10.1073/pnas.97.8.4092 | issue=8 | pmid=10760278 | pmc = 18159 |bibcode=2000PNAS...97.4092B |doi-access=free }}</ref> because the gnetophytes' specialization to their respective environments is so complete that they hardly resemble each other at all. ''Gnetum'' species are mostly [[Woody plant|woody]] vines in tropical forests, though the best-known member of this group, ''[[Gnetum gnemon]]'',<ref name="wan">Wan T, Liu Z M, Li L F, et al. A genome for gnetophytes and early evolution of seed plants[J]. Nature plants, 2018, 4(2): 82. </ref> is a tree native to western [[Malesia]]. The one remaining species of ''Welwitschia'', ''[[Welwitschia mirabilis]]'', native only to the dry deserts of [[Namibia]] and [[Angola]], is a ground-hugging species with only two large strap-like leaves that grow continuously from the base throughout the plant's life. ''Ephedra'' species, known as "jointfirs" in the United States, have long slender branches which bear tiny scale-like leaves at their nodes. Infusions from these plants have been traditionally used as a [[stimulant]], but [[ephedrine]] is a [[controlled substance]] today in many places because of the risk of harmful or even fatal [[overdose|overdosing]].
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