Editing Gnetophyta

{{Short description|Division of plants containing three genera of gymnosperms}}
{{Automatic taxobox
| image = Gnetum luofuense 125787614.jpg
| fossil_range = {{fossil range|Jurassic|recent|earliest=Roadian}}
| image_caption = ''[[Gnetum luofuense]]'' with female cones
| image2 = Welwitschia at Ugab River basin.jpg
| image2_caption = ''[[Welwitschia mirabilis]]'' female plant with cones
| parent_authority = Bessey 1907
| taxon = Gnetopsida
| authority = Thom 1886
| subdivision_ranks = Families and genera
| subdivision = [[Gnetaceae]]<br/>
&nbsp;&nbsp;''[[Gnetum]]''<br/>
[[Welwitschiaceae]]<br/>
&nbsp;&nbsp;''[[Welwitschia]]''<br/>
[[Ephedraceae]]<br/>
&nbsp;&nbsp;''[[Ephedra (genus)|Ephedra]]''
| range_map = Gnetophyta distribution genera separate.PNG
| range_map_alt = A distribution map of Gnetophyta colour-coded by genus
| range_map_caption = Distribution, separated by genus: <br/>Green – ''Welwitschia''<br/>Blue – ''Gnetum''<br/>Red – ''Ephedra''<br/>Purple – ''Gnetum'' and ''Ephedra''
}}

'''Gnetophyta''' ({{IPAc-en|n|ɛ|ˈ|t|ɒ|f|ᵻ|t|ə|,_|ˈ|n|ɛ|t|oʊ|f|aɪ|t|ə}}) is a division of plants (alternatively considered the subclass '''Gnetidae''' or order '''Gnetales'''), grouped within the [[gymnosperm]]s (which also includes [[conifer]]s, [[cycad]]s, and [[ginkgo]]s), that consists of some 70 species across the three [[Relict (biology)|relict]] [[genus|genera]]: ''[[Gnetum]]'' ([[Family (biology)|family]] Gnetaceae), ''[[Welwitschia]]'' (family [[Welwitschiaceae]]), and ''[[Ephedra (genus)|Ephedra]]'' (family [[Ephedraceae]]). The earliest unambiguous records of the group date to the [[Jurassic]], and they achieved their highest diversity during the [[Early Cretaceous]]. The primary difference between gnetophytes and other [[gymnosperm]]s is the presence of [[vessel element]]s, a system of small tubes ([[xylem]]) that transport water within the plant, similar to those found in [[flowering plant]]s. Because of this, gnetophytes were once thought to be the closest gymnosperm relatives to flowering plants, but more recent molecular studies have brought this hypothesis into question, with many recent phylogenies finding them to be nested within the conifers.

Though it is clear they are all related, the exact evolutionary inter-relationships between gnetophytes are unclear. Some classifications hold that all three genera should be placed in a single [[Order (biology)|order]] (Gnetales), while other classifications say they should be distributed among three separate orders, each containing a single family and genus. Most morphological and molecular studies confirm that the genera ''Gnetum'' and ''Welwitschia'' diverged from each other more recently than they did from [[Ephedra (plant)|''Ephedra''.]]<ref name="crane">{{cite journal | title = Fossils and plant phylogeny |author1=Peter R. Crane |author2=Patrick Herendeen |author3=Else Marie Friis |author-link3=Else Marie Friis | journal = American Journal of Botany | year = 2004 | volume = 91 | pages = 1683–1699  | doi = 10.3732/ajb.91.10.1683 | issue=10 | pmid = 21652317| doi-access = free }}</ref><ref name="Bowe" /><ref name="Gugerli">{{cite journal | title = The evolutionary split of Pinaceae from other conifers: evidence from an intron loss and a multigene phylogeny |author1=Gugerli, F. |author2=Sperisen, C. |author3=Buchler, U. |author4=Brunner, L. |author5=Brodbeck, S. |author6=Palmer, J.D. |author7=Qiu, Y.L. | journal = Molecular Phylogenetics and Evolution | year = 2001 | volume = 21 | pages = 167–175 | doi = 10.1006/mpev.2001.1004 | pmid = 11697913 | issue = 2}}</ref><ref name="Rai">{{cite journal|title=Inference of higher-order conifer relationships from a multi-locus plastid data set |author1=Rai, H.S. |author2=Reeves, P.A. |author3=Peakall, R. |author4=Olmstead, R.G. |author5=Graham, S.W. |journal=Botany |year=2008 |volume=86 |pages=658–669 |doi=10.1139/B08-062 |issue=7 }}</ref><ref name="Ickert-Bond">{{cite journal | title = A fossil-calibrated relaxed clock for Ephedra indicates an Oligocene age for the divergence of Asian and New World clades, and Miocene dispersal into South America | author = Ickert-Bond, S. M. | author2 = C. Rydin | author3 = S. S. Renner | name-list-style = amp | journal = Journal of Systematics and Evolution  | year = 2009 | volume = 47 | issue = 5 | pages = 444–456  | url = http://onlinelibrary.wiley.com/store/10.1111/j.1759-6831.2009.00053.x/asset/j.1759-6831.2009.00053.x.pdf?v=1&t=h3tses6s&s=16e93aab7f364e4fc976943373d12ae7d30d34a7 | doi=10.1111/j.1759-6831.2009.00053.x| s2cid = 55148071 | doi-access = free }}</ref>
[[File:Welwitschia mirabilis S&J6.jpg|thumb|''Welwitschia mirabilis'' bearing male cones]]
[[File:Ephedra distachya (male flowers) 1.jpg|thumb|''Ephedra distachya'' (male cones)]]
[[File:Ephedra distachya (female plant in bloom).jpg|thumb|''Ephedra distachya'' (female plant in bloom)]]
[[File:Gnetum gnemon male.jpg|thumb|''Gnetum gnemon'' male strobili]]
[[File:Gnetum gnemon BotGardBln1105C.JPG|thumb|''Gnetum gnemon'' female strobilus]]
[[File:Female Ephedra californica cone - journal.pone.0053652.g002-A.png|thumb|Female ''[[Ephedra californica]]'' cone]]

==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 = 489–515 | 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 = 4092–4097 | 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]].

==Classification==
With just three well-defined genera within an entire division, there still is understandable difficulty in establishing an unambiguous interrelationship among them; in earlier times matters were even more difficult, with Pearson in the early 20th century discussing about the [[Class (biology)|class]] Gnetales, rather than the order.<ref name=PearsonH>
{{cite book
 |author=Pearson, H.H.W.
 |orig-year=1929  |year=2010
 |title=Gnetales
 |publisher=Cambridge University Press
 |isbn=978-1108013987
}}
</ref> G.H.M. Lawrence referred to them as an order, but remarked that the three families were distinct enough to deserve recognition as separate orders.<ref name="GHML">Lawrence, George Hill Mathewson. Taxonomy of vascular plants. Macmillan, 1951</ref> Foster & Gifford accepted this principle, and placed the three orders together in a common class for convenience, which they called Gnetopsida.<ref name="FosGif">
{{cite book
 |author1=Foster, Adriance S.
 |author2=Gifford, Ernest M. Jr.
 |year=1974
 |title=Comparative Morphology of Vascular Plants
 |publisher=Freeman
 |isbn=0-7167-0712-8
}}
</ref> In general the evolutionary relationships among the [[spermatophyte|seed plants]] still are unresolved, and the Gnetophyta have played an important role in the formation of [[phylogenetics|phylogenetic]] hypotheses. 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 [[Glossopteridales|glossopterids]]. When these gymnosperm fossils are considered, the question of gnetophyte relationships to other seed plants becomes even more complicated. Several hypotheses, illustrated below, have been presented to explain seed plant evolution. Some morphological studies have supported a close relationship between Gnetophyta, [[Bennettitales]] and the [[Erdtmanithecales]].<ref>
{{Cite journal
 |last1=Friis      |first1=Else Marie        |last2=Crane    |first2=Peter R.
 |last3=Pedersen   |first3=Kaj Raunsgaard    |last4=Bengtson |first4=Stefan
 |last5=Donoghue   |first5=Philip C.J.       |last6=Grimm    |first6=Guido W.
 |last7=Stampanoni |first7=Marco
 |date=November 2007
 |title=Phase-contrast X-ray microtomography links Cretaceous seeds with Gnetales and Bennettitales 
 |journal=Nature
 |volume=450 |issue=7169 |pages=549–552
 |doi=10.1038/nature06278 |pmid=18033296 |bibcode=2007Natur.450..549F
 |s2cid=1198220 |issn=0028-0836
}}
</ref>

Recent research by Lee, Cibrian-Jaramillo, ''et al.'' (2011) suggests that the Gnetophyta are a sister group to the rest of the gymnosperms,<ref name=lee>
{{cite journal
 | author1=Lee, E.K.          | author2=Cibrian-Jaramillo, A.
 | author3=Kolokotronis, S.O. | author4=Katari, M.S.
 | author5=Stamatakis, A.   | display-authors=etal
 | year = 2011
 | title = A functional phylogenomic view of the seed plants
 | journal = PLOS Genet
 | volume = 7  | issue = 12  | page = e1002411
 | doi = 10.1371/journal.pgen.1002411 | pmid=22194700 | pmc=3240601
| doi-access=free
 }}</ref> contradicting the anthophyte hypothesis, which held that gnetophytes were sister to the flowering plants.

===Gnetifer hypothesis===
In the gnetifer hypothesis, the gnetophytes are sister to the [[conifer]]s, and the [[gymnosperm]]s are a [[monophyletic]] group, sister to the angiosperms.The gnetifer hypothesis first emerged formally in the mid-twentieth century, when vessel elements in the gnetophytes were interpreted as being derived from [[tracheid]]s with circular bordered pits, as in conifers.<ref name=Judd/> It however only gained strong support with the emergence of molecular data in the late 1990s.<ref name=Chaw/><ref name="Qui">
{{cite journal |author1=Qiu, Y.L. |author2=Lee, J. |author3=Bernasconi-Quadroni, F. |author4=Soltis, D.E. |author5=Soltis, P.S. |author6=Zanis, M. |author7=Zimmer, E.A. |author8=Chen, Z. |author9=Savalainen, V. |author10=Chase, M.W. |name-list-style=amp |year=1999 |title=The earliest angiosperms: evidence from mitochondrial, plastid and nuclear genomes |journal=Nature |volume=402 |issue=6760 |pages=404–407 |bibcode=1999Natur.402..404Q |doi=10.1038/46536 |pmid=10586879 |s2cid=4380796}}
</ref><ref name=Rydin>
{{cite journal
 | author1=Rydin, C.
 | author2=Kallersjo, M.
 | author3=Friist, E.M.
 | year = 2002
 | title = Seed plant relationships and the systematic position of Gnetales based on nuclear and chloroplast DNA: Conflicting data, rooting problems, and the monophyly of conifers
 | journal = International Journal of Plant Sciences
 | volume = 163  | issue = 2  | pages = 197–214
 | doi = 10.1086/338321 | jstor=3080238 |s2cid=84578578
}}
</ref><ref name=Braukmann>
{{cite journal
 |author1=Braukmann, T.W.A.
 |author2=Kuzmina, M.
 |author3=Stefanovic, S.
 | year = 2009
 | title = Loss of all plastid nhd genes in Gnetales and conifers: Extent and evolutionary significance for the seed plant phylogeny
 | journal = Current Genetics
 | volume = 55 | issue = 3 | pages = 323–337
 | doi = 10.1007/s00294-009-0249-7 | pmid = 19449185 | s2cid = 3939394
 | url = http://www.nature.com/nrg/journal/v2/n3/full/nrg0301_186a.html
| url-access = subscription
 }}
</ref> Although the most salient morphological evidence still largely supports the anthophyte hypothesis, some more obscure morphological commonalities between the gnetophytes and conifers lend support to the gnetifer hypothesis.These shared traits include: [[tracheids]] with scalariform pits with tori interspersed with annular thickenings, absence of scalariform pitting in primary [[xylem]], scale-like and strap-shaped [[leaf|leaves]] of ''[[Ephedra (plant)|Ephedra]]'' and ''[[Welwitschia]]''; and reduced [[sporophyll]]s.<ref name="Magallon">
{{cite journal |author1=Magallon, S. |author2=Sanderson, M.J. |year=2002 |title=Relationships among seed plants inferred from highly conserved genes: sorting conflicting phylogenetic signals among ancient lineages |journal=American Journal of Botany |volume=89 |issue=12 |pages=1991–2006 |doi=10.3732/ajb.89.12.1991 |jstor=4122754 |pmid=21665628 |doi-access=free}}
</ref><ref name="Sanderson">
{{cite journal |author1=Sanderson, M.J. |author2=Wojciechowski, M.F. |author3=Hu, J.M. |author4=Sher Khan, T. |author5=Brady, S.G. |year=2000 |title=Error, bias, and long-branch attraction in data for two chloroplast photosystem genes in seed plants |journal=Molecular Biology and Evolution |volume=17 |issue=5 |pages=782–797 |doi=10.1093/oxfordjournals.molbev.a026357 |pmid=10779539 |doi-access=free}}
</ref><ref name=Burleigh>
{{cite journal
 | author1 = Burleigh, J.G.
 | author2 = Mathews, S.
 | year = 2007
 | title = Phylogenetic signal in nucleotide data from seed plants: Implications for resolving the seed plant tree of life
 | journal =  American Journal of Botany
 | volume = 168 | issue = 10 | pages = 125–135
 | pmid = 21652311
 | doi = 10.3732/ajb.91.10.1599 | doi-access = free
 }}
</ref>

{{clade 
  |1=angiosperms (flowering plants)
  |label2=gymnosperms
  |2={{clade 
    |1=cycads  
    |2=''Ginkgo'' 
    |label3=“'''Gnetifers'''”
    |3={{clade 
        |1=conifers 
        |2=gnetophytes
    }}
  }}
}}

===Anthophyte hypothesis===
From the early twentieth century, the anthophyte hypothesis was the prevailing explanation for [[seed plant]] evolution, based on shared [[morphology (biology)|morphological]] characters between the gnetophytes and angiosperms. In this hypothesis, the gnetophytes, along with the extinct order Bennettitales, are sister to the angiosperms, forming the "anthophytes".<ref name=Judd/> Some morphological characters that were suggested to unite the anthophytes include vessels in wood, net-veined leaves (in ''[[Gnetum]]'' only), [[lignin]] chemistry, the layering of cells in the apical [[meristem]], [[pollen]] and [[megaspore]] features (including thin megaspore wall), short cambial initials, and lignin syringal groups.<ref name=Judd/><ref name=Donaghue>
{{cite journal
 | author1 = Donoghue, M.J.
 | author2 = Doyle, J.A.
 | year = 2000
 | title = Seed plant phylogeny: demise of the anthophyte hypothesis?
 | journal = Current Biology
 | volume = 10 | issue = 3 | pages = R106–R109
 | doi = 10.1016/S0960-9822(00)00304-3
 | pmid = 10679315 |s2cid=16558206
| doi-access = free
 | bibcode = 2000CBio...10.R106D
 }}
</ref><ref name=Loconte>
{{cite journal
 | author1 = Loconte, H.
 | author2 = Stevenson, D.W.
 | year = 1990
 | title = Cladistics of the Spermatophyta
 | journal = Brittonia
 | volume = 42 | issue = 3 | pages = 197–211
 | doi = 10.2307/2807216 | jstor = 2807216
 | bibcode = 1990Britt..42..197L
 |s2cid=36908568
}}
</ref><ref name=Nixon>
{{cite journal
 | author1 = Nixon, K.C.    | author2 = Crepet, W.L.
 | author3 = Stevenson, D.  | author4 = Friis, E.M.
 | year = 1994
 | title = A reevaluation of seed plant phylogeny
 | journal = Annals of the Missouri Botanical Garden
 | volume = 81 | issue = 3 | pages = 494–533
 | doi = 10.2307/2399901 | jstor=2399901
 | url=https://www.biodiversitylibrary.org/part/30316
}}
</ref> However, most genetic studies, as well as more recent morphological analyses,<ref name=Coiro>
{{cite journal
 | author1 = Coiro, M.
 | author2 = Chomicki, G.
 | author3 = Doyle, J.A.
 | year = 2018
 | title = Experimental signal dissection and method sensitivity analyses reaffirm the potential of fossils and morphology in the resolution of the relationship of angiosperms and Gnetales
 | journal = Paleobiology
 | volume = 44 | issue = 3  | pages =  490–510
 | doi = 10.1017/pab.2018.23 | bibcode = 2018Pbio...44..490C
 |s2cid=91488394
}}
</ref> have rejected the anthophyte hypothesis.<ref name="Bowe" /><ref name="Chaw">
{{cite journal
 | author1 = Chaw, S.M.  | author2 = Aharkikh, A.
 | author3 = Sung, H.M.  | author4 = Lau, T.C.
 | author5 = Li, W.H.
 | year = 1997
 | title = Molecular phylogeny of extant gymnosperms and seed plant evolution: Analysis of nuclear 18S rRNA sequences
 | journal = Molecular Biology and Evolution
 | volume = 14 | issue = 1 | pages = 56–68
 | pmid = 9000754
 | doi=10.1093/oxfordjournals.molbev.a025702 | doi-access = free
}}
</ref><ref name="Qui" /><ref name="Magallon" /><ref name="Sanderson" /><ref name = "Chaw2">
{{cite journal
 | author1 = Chaw, S.M.   | author2 = Parkinson, C.L.
 | author3 = Cheng, Y.    | author4 = Vincent, T.M.
 | author5 = Palmer, J.D.
 | year = 2000
 | title = Seed plant phylogeny inferred from all three plant genomes: Monophyly of extant gymnosperms and origin of Gnetales from conifers
 | journal = Proceedings of the National Academy of Sciences USA
 | volume = 97 | issue=8 | pages = 4086–4091
 | doi = 10.1073/pnas.97.8.4086 | pmid=10760277
 | pmc=18157 |bibcode=2000PNAS...97.4086C
| doi-access = free
 }}
</ref><ref name=Goremykin>
{{cite journal
 | author1 = Goremykin, V.   | author2 = Bobrova, V.
 | author3 = Pahnke, J.      | author4 = Troitsky, A.
 | author5 = Antonov, A.     | author6 = Martin, W.
 | year = 1996
 | title = Noncoding sequences from the slowly evolving chloroplast inverted repeat in addition to rbcL data do not support gnetalean affinities of angiosperms
 | journal = Molecular Biology and Evolution
 | volume = 13  | issue = 2  | pages = 383–396
 | pmid = 8587503
 | doi=10.1093/oxfordjournals.molbev.a025597 | doi-access = free
}}
</ref><ref name=Hajibabaei>
{{cite journal
 | author1 = Hajibabaei, M.
 | author2 = Xia, J.
 | author3 = Drouin, G.
 | year = 2006
 | title = Seed plant phylogeny: Gnetophytes are derived conifers and a sister group to Pinaceae
 | journal = Molecular Phylogenetics and Evolution
 | volume = 40  | issue = 1  | pages = 208–217
 | doi = 10.1016/j.ympev.2006.03.006 | pmid = 16621615
}}</ref><ref name=Hansen>
{{cite journal
 | author1 = Hansen, A.       | author2 = Hansmann, S.
 | author3 = Samigullin, T.   | author4 = Antonov, A.
 | author5 = Martin, W.
 | year = 1999
 | title = Gnetum and the angiosperms: molecular evidence that their shared morphological characters are convergent rather than homologous
 | journal = Molecular Biology and Evolution
 | volume = 16  | issue = 7  | pages = 1006–1009
 | doi=10.1093/oxfordjournals.molbev.a026176  | doi-access = free
}}
</ref><ref name=Samigullin>
{{cite journal
 | author1=Samigullin, T.K.   | author2=Martin, W.F.
 | author3=Troitsky, A.V.     | author4=Antonov, A.S.
 | year = 1999
 | title = Molecular data from the chloroplast rpoC1 gene suggest a deep and distinct dichotomy of contemporary spermatophytes into two monophyla: gymnosperms (including Gnetalaes) and angiosperms
 | journal = Journal of Molecular Evolution
 | volume = 49  | issue = 3  | pages = 310–315
 | doi = 10.1007/PL00006553
 |bibcode=1999JMolE..49..310S  |s2cid=4232968  | pmid = 10473771
}}
</ref>{{Excessive citations inline|date=January 2022}}

Several of these studies have suggested that the gnetophytes and angiosperms have independently derived characters, including flower-like reproductive structures and tracheid vessel elements, that appear shared but are actually the result of parallel evolution.<ref name="Bowe" /><ref name="Judd" /><ref name="Chaw2" />

{{clade 
  |1=''Ginkgo'' 
  |2=cycads  
  |3=[[conifer]]s 
  |label4=anthophytes
  |4={{clade 
    |1=angiosperms (flowering plants)  
    |2=gnetophytes
  }}
}}

===Gnepine hypothesis===
The gnepine hypothesis is a modification of the gnetifer hypothesis, and suggests that the gnetophytes belong within the conifers as a sister group to the [[Pinaceae]].<ref name=Judd/> According to this hypothesis, the conifers as currently defined are not a monophyletic group, in contrast with molecular findings that support its monophyly.<ref name=Rydin/> All existing evidence for this hypothesis comes from molecular studies since 1999.<ref name=Bowe/><ref name=Gugerli/><ref name=Chaw2/><ref name=Hajibabaei/><ref name=Magallon/><ref name=Qui/><ref name=Sanderson/><ref name=Burleigh/><ref name=Ran2018>{{cite journal|doi=10.1098/rspb.2018.1012|title=Phylogenomics resolves the deep phylogeny of seed plants and indicates partial convergent or homoplastic evolution between Gnetales and angiosperms|year=2018|last1=Ran|first1=Jin-Hua|last2=Shen|first2=Ting-Ting|last3=Wang|first3=Ming-Ming|last4=Wang|first4=Xiao-Quan|journal=Proceedings of the Royal Society B: Biological Sciences|volume=285|issue=1881|pmid=29925623|pmc=6030518}}</ref><ref name=Stull2021>{{cite journal|doi=10.1038/s41477-021-00964-4|title=Gene duplications and phylogenomic conflict underlie major pulses of phenotypic evolution in gymnosperms|year=2021|last1=Stull|first1=Gregory W.|last2=Qu|first2=Xiao-Jian|last3=Parins-Fukuchi|first3=Caroline|last4=Yang|first4=Ying-Ying|last5=Yang|first5=Jun-Bo|last6=Yang|first6=Zhi-Yun|last7=Hu|first7=Yi|last8=Ma|first8=Hong|last9=Soltis|first9=Pamela S.|last10=Soltis|first10=Douglas E.|last11=Li|first11=De-Zhu|last12=Smith|first12=Stephen A.|last13=Yi|first13=Ting-Shuang|journal=Nature Plants|volume=7|issue=8|pages=1015–1025|pmid=34282286|s2cid=236141481}}</ref> A 2018 phylogenomic study estimated the divergence between Gnetales and Pinaceae at around 241 millions of years ago, in the early [[Triassic]]<ref name=Ran2018/> while a 2021 study placed it earlier, in the [[Carboniferous]].<ref name=Stull2021/>

However, the morphological evidence remains difficult to reconcile with the gnepine hypothesis. If the gnetophytes are nested within conifers, they must have lost several shared derived characters of the conifers (or these characters must have evolved in parallel in the other two conifer lineages): narrowly triangular leaves (gnetophytes have diverse leaf shapes), [[resin]] canals, a tiered [[proembryo]], and flat woody ovuliferous [[Conifer cone|cone]] scales.<ref name=Magallon/> These kinds of major morphological changes are not without precedent in the [[Pinales]], however: the [[Taxaceae]], for example, have lost the classical cone of the conifers in favor of a single-terminal ovule, surrounded by a fleshy aril.<ref name=Chaw2/>

{{clade 
  |1=[[angiosperm]]s (flowering plants)
  |label2=[[gymnosperm]]s  
  |2={{clade 
    |1=[[cycad]]s 
    |2=''[[Ginkgo]]'' 
    |label3=[[conifer]]s
    |3={{clade 
      |label1=“'''Gnepines'''”
      |1={{clade 
        |1=[[Pinaceae]] (the pine family) 
        |2=[[gnetophytes]]
      }} 
      |2=(other conifers)
    }}
  }}
}}

===Gnetophyte-sister hypothesis===
Some partitions of the genetic data suggest that the gnetophytes are sister to all of the other extant seed plant groups.<ref name=Rai/><ref name=Judd/><ref name=Magallon/><ref name=Sanderson/><ref name=Rydin/><ref name=Yinzhi>
{{cite news
 |last1=Zhang |first1=Y
 |last2=Liu   |first2=Z.
 |date=7 May 2019
 |title=Genic evidence that gnetophytes are sister to all other seed plants
 |website=bioRxiv
 |id=bioRxiv 629915
 |type=preprint
 |publisher=Cold Springs Harbor Laboratory
 |doi=10.1101/629915
}}
</ref><ref name=Chen>
{{cite journal
 |last1=Chen |first1=Z.-D.   |last2=Yang |first2=T.
 |last3=Lin  |first3=L.      |last4=Lu   |first4=L.-M.
 |last5=Li   |first5=H.-L.
 |last6=Sun  |first6=M.    |display-authors=etal
 |year=2016
 |title=Tree of life for the genera of Chinese vascular plants
 |journal=Journal of Systematics and Evolution
 |volume=54 |issue=4 |pages=277–306
  |doi=10.1111/jse.12219
|doi-access=free}}
</ref> However, there is no morphological evidence nor examples from the fossil record to support the gnetophyte-sister hypotheses.<ref name=Burleigh/>

{{clade 
  |1=[[gnetophytes]]
  |2={{clade 
    |1=angiosperms (flowering plants)
    |2={{clade 
      |1=cycads  
      |2=''Ginkgo'' 
      |3=conifers
    }}
  }}
}}

== Fossil gnetophytes ==
Knowledge of gnetophyte history through fossil discovery has increased greatly since the 1980s.<ref name="crane" /> Although some fossils that have been proposed to be gnetophytes have been found as far back as the [[Permian]],<ref name="Zi-Qiang Wang-2004">{{cite journal |author=Zi-Qiang Wang |year=2004 |title=A New Permian Gnetalean Cone as Fossil Evidence for Supporting Current Molecular Phylogeny |url= |journal=Annals of Botany |volume=94 |issue=2 |pages=281–288 |doi=10.1093/aob/mch138 |pmc=4242163 |pmid=15229124}}</ref> their affinities to the group are equivocal. The oldest fossils that are definitely assignable to the group date to the Late Jurassic.<ref name="Coiro-2022">{{Cite journal |last1=Coiro |first1=Mario |last2=Roberts |first2=Emily A. |last3=Hofmann |first3=Christa-Ch. |last4=Seyfullah |first4=Leyla J. |date=2022-12-14 |title=Cutting the long branches: Consilience as a path to unearth the evolutionary history of Gnetales |journal=Frontiers in Ecology and Evolution |volume=10 |pages=1082639 |doi=10.3389/fevo.2022.1082639 |issn=2296-701X|doi-access=free }}</ref> Overall, the fossil record of the group is richest during the [[Early Cretaceous]], exhibiting a substantial decline during the Late Cretaceous.<ref name="Coiro-2022" />

Ephedraceae
*''[[Leongathia]]'' V.A. Krassilov, D.L. Dilcher & J.G. Douglas 1998<ref>{{Cite journal|last1=Krassilov|first1=V.A.|last2=Dilcher|first2=D.L.|last3=Douglas|first3=J.G.|date=January 1998|title=New ephedroid plant from the Lower Cretaceous Koonwarra Fossil Bed, Victoria, Australia|url=http://www.tandfonline.com/doi/abs/10.1080/03115519808619195|journal=Alcheringa: An Australasian Journal of Palaeontology|language=en|volume=22|issue=2|pages=123–133|doi=10.1080/03115519808619195|bibcode=1998Alch...22..123K |issn=0311-5518|url-access=subscription}}</ref> [[Koonwarra, Victoria|Koonwarra fossil bed]], Australia, Early Cretaceous ([[Aptian]])
*''[[Jianchangia]]'' Yang, Wang and Ferguson, 2020<ref>{{Cite journal|last1=Yang|first1=Yong|last2=Wang|first2=Yingwei|last3=Ferguson|first3=David Kay|date=2020-02-04|title=A new macrofossil ephedroid plant with unusual bract morphology from the Lower Cretaceous Jiufotang Formation of northeastern China|url= |journal=BMC Evolutionary Biology|volume=20|issue=1|pages=19|doi=10.1186/s12862-019-1569-y|issn=1471-2148|pmc=7001366|pmid=32019502 |doi-access=free |bibcode=2020BMCEE..20...19Y }}</ref> [[Jiufotang Formation]], China, Early Cretaceous (Aptian)
*''[[Eamesia]]'' Yang, Lin and Ferguson, 2018<ref>{{Cite journal|last1=Yang|first1=Yong|last2=Lin|first2=Longbiao|last3=Ferguson|first3=David K.|last4=Wang|first4=Yingwei|date=December 2018|title=Macrofossil evidence unveiling evolution of male cones in Ephedraceae (Gnetidae)|url= |journal=BMC Evolutionary Biology|language=en|volume=18|issue=1|pages=125|doi=10.1186/s12862-018-1243-9|issn=1471-2148|pmc=6116489|pmid=30157769 |doi-access=free |bibcode=2018BMCEE..18..125Y }}</ref> [[Yixian Formation]], China, Early Cretaceous (Aptian)
*''[[Prognetella]]'' Krassilov et Bugdaeva, 1999 Yixian Formation, China, Early Cretaceous (Aptian) (initially interpreted as an angiosperm)<ref>{{Cite journal|last1=Yang|first1=Yong|last2=Ferguson|first2=David K.|date=October 2015|title=Macrofossil evidence unveiling evolution and ecology of early Ephedraceae|url=https://linkinghub.elsevier.com/retrieve/pii/S1433831915000657|journal=Perspectives in Plant Ecology, Evolution and Systematics|language=en|volume=17|issue=5|pages=331–346|doi=10.1016/j.ppees.2015.06.006|url-access=subscription}}</ref>
*''[[Chengia]]'' Yang, Lin & Wang, 2013,<ref>{{Cite journal|last1=Yang|first1=Yong|last2=Lin|first2=Longbiao|last3=Wang|first3=Qi|date=2013-03-27|title=Chengia laxispicatagen. et sp. nov., a new ephedroid plant from the Early Cretaceous Yixian Formation of western Liaoning, Northeast China: evolutionary, taxonomic, and biogeographic implications|url= |journal=BMC Evolutionary Biology|volume=13|issue=1|pages=72|doi=10.1186/1471-2148-13-72|issn=1471-2148|pmc=3626868|pmid=23530702 |doi-access=free |bibcode=2013BMCEE..13...72Y }}</ref> Yixian Formation, China, Early Cretaceous (Aptian)
*''[[Chaoyangia (plant)|Chaoyangia]]'' Duan, 1998  Yixian Formation, China, Early Cretaceous (Aptian)
*''[[Eragrosites]]'' Yixian Formation, China, Early Cretaceous (Aptian)
*''[[Gurvanella]]'' China, Mongolia, Early Cretaceous
*''[[Alloephedra]]'' China, Early Cretaceous
*''[[Amphiephedra]]'' China, Early Cretaceous
*''[[Beipiaoa]]'' China, Early Cretaceous
*''[[Ephedrispermum]]'' Portugal, Early Cretaceous (Aptian-Albian)
*''[[Ephedrites]]'' China, Early Cretaceous
*''[[Erenia]]'' China, Mongolia, Early Cretaceous
*''[[Liaoxia]]'' China, Early Cretaceous
*''[[Dichoephedra]]'' China, Early Cretaceous
*''[[Laiyangia]]'' P.H. Jin, 2024<ref>{{Cite journal |last1=Jin |first1=Peihong |last2=Zhang |first2=Mingzhen |last3=Du |first3=Baoxia |last4=Zhang |first4=Jing |last5=Sun |first5=Bainian |date=March 2024 |title=A new gnetalean macrofossil from the Lower Cretaceous of the Laiyang Basin, eastern China |journal=Plant Diversity |volume=46 |issue=5 |pages=678–682 |language=en |doi=10.1016/j.pld.2024.03.002|doi-access=free |pmid=39290879 |pmc=11403114 }}</ref> China, Early Cretaceous
Gnetaceae 
*''[[Khitania]]'' Guo et al. 2009<ref>{{Cite journal|last1=Guo|first1=Shuang-Xing|last2=Sha|first2=Jin-Geng|last3=Bian|first3=Li-Zeng|last4=Qiu|first4=Yin-Long|date=March 2009|title=Male spike strobiles with Gnetum affinity from the Early Cretaceous in western Liaoning, Northeast China|journal=Journal of Systematics and Evolution|language=en|volume=47|issue=2|pages=93–102|doi=10.1111/j.1759-6831.2009.00007.x|doi-access=free|hdl=2027.42/74128|hdl-access=free}}</ref> Yixian Formation, China, Early Cretaceous (Aptian)
Welwitschiaceae 
*''[[Priscowelwitschia]]'' Dilcher et al., 2005 [[Crato Formation]], Brazil, Early Cretaceous (Aptian)
*''[[Cratonia]]'' Rydin et al., 2003 Crato Formation, Brazil, Early Cretaceous (Aptian)
*''[[Welwitschiostrobus]]'' Dilcher et al., 2005 Crato Formation, Brazil, Early Cretaceous (Aptian)
''Incertae sedis'': 
*''[[Archangelskyoxylon]]''  Brea, Gnaedinger & Martínez, 2023  [[Roca Blanca Formation]], Argentina, [[Sinemurian]]–[[Toarcian]] (closely related to Weltwitschia and Gnetum).<ref>{{cite journal |last1=Brea|first1=Mariana |last2=Silvia |first2=Gnaedinger |last3=Martínez |first3=Leandro C.A. |title=Archangelskyoxylon carlquistii gen. et sp. nov. Taxonomy and phylogeny of an unequivocal gnetoid Jurassic fossil wood |journal=Review of Palaeobotany and Palynology |date=2023 |issue=105035 |url=https://www.sciencedirect.com/science/article/pii/S003466672300204 |access-date=29 November 2023}}</ref>
*''[[Drewria]]'' Crane & Upchurch, 1987 [[Potomac Group]], USA, [[Albian]] (possible affinities to Welwitschiaceae)<ref name="Friis-2014">{{Cite journal|last1=Friis|first1=Else Marie|last2=Pedersen|first2=Kaj Raunsgaard|last3=Crane|first3=Peter R.|date=2014-07-03|title=Welwitschioid diversity in the Early Cretaceous: evidence from fossil seeds with pollen from Portugal and eastern North America|journal=Grana|language=en|volume=53|issue=3|pages=175–196|doi=10.1080/00173134.2014.915980|issn=0017-3134|doi-access=free|bibcode=2014Grana..53..175F |hdl=20.500.11850/96968|hdl-access=free}}</ref>
*''[[Bicatia]]'' Friis, Pedersen and Crane, 2014<ref name="Friis-2014" /> [[Figueira da Foz Formation]], Portugal, Early Cretaceous (late Aptian early Albian), [[Potomac Group]], USA, Albian (possible affinities to Welwitschiaceae)
*''[[Liaoningia]]'' Yang et al, 2017<ref>{{Cite journal|last1=Yang|first1=Yong|last2=Lin|first2=Long-Biao|last3=Ferguson|first3=David K.|last4=Zhang|first4=Shou-Zhou|last5=Wan|first5=Tao|date=June 2017|title=A new gnetalean macrofossil from the Early Cretaceous and its evolutionary significance|url=https://linkinghub.elsevier.com/retrieve/pii/S0195667116302853|journal=Cretaceous Research|language=en|volume=74|pages=56–64|doi=10.1016/j.cretres.2017.02.007|bibcode=2017CrRes..74...56Y |url-access=subscription}}</ref> Yixian Formation, China, Early Cretaceous (Aptian)
*''[[Protognetum]]'' Y. Yang, L. Xie et D.K. Ferguson, 2017<ref>{{Cite journal|last1=Yang|first1=Yong|last2=Xie|first2=Lei|last3=Ferguson|first3=David K.|date=October 2017|title=Protognetaceae: A new gnetoid macrofossil family from the Jurassic of northeastern China|url=https://linkinghub.elsevier.com/retrieve/pii/S1433831916301652|journal=Perspectives in Plant Ecology, Evolution and Systematics|language=en|volume=28|pages=67–77|doi=10.1016/j.ppees.2017.08.001|url-access=subscription}}</ref> [[Daohugou Bed]], China, Middle Jurassic ([[Callovian]])
*''[[Itajuba (plant)|Itajuba]]'' Ricardi-Branco et al, 2013,<ref>{{Citation|last1=Ricardi-Branco|first1=Fresia|title=Itajuba yansanae Gen and SP NOV of Gnetales, Araripe Basin (Albian-Aptian) in Northeast Brazil|date=2013-05-22|url=http://www.intechopen.com/books/climate-change-and-regional-local-responses/itajuba-yansanae-gen-and-sp-nov-of-gnetales-araripe-basin-albian-aptian-in-northeast-brazil|work=Climate Change and Regional/Local Responses|editor-last=Ray|editor-first=Pallav|publisher=InTech|language=en|doi=10.5772/55704|isbn=978-953-51-1132-0|access-date=2020-12-05|last2=Torres|first2=Margarita|last3=S.|first3=Sandra|last4=de Souza|first4=Ismar|last5=E. Tavares|first5=Paulo G.|last6=Arruda Campos|first6=Antonio C.|doi-access=free}}</ref> Crato Formation, Brazil, Early Cretaceous (Aptian)
*''[[Protoephedrites]]'' Rothwell et Stockey, 2013<ref>{{Cite journal|last1=Rothwell|first1=Gar W.|last2=Stockey|first2=Ruth A.|date=March 2013|title=Evolution and Phylogeny of Gnetophytes: Evidence from the Anatomically Preserved Seed Cone Protoephedrites eamesii gen. et sp. nov. and the Seeds of Several Bennettitalean Species|url=https://www.journals.uchicago.edu/doi/10.1086/668688|journal=International Journal of Plant Sciences|language=en|volume=174|issue=3|pages=511–529|doi=10.1086/668688|s2cid=84063572|issn=1058-5893|url-access=subscription}}</ref> Canada, [[Valanginian]] (possible ephedroid affinities) 
*''[[Siphonospermum]]'' Rydin et Friis, 2010<ref>{{Cite journal|last1=Rydin|first1=Catarina|last2=Friis|first2=Else Marie|date=2010-06-17|title=A new Early Cretaceous relative of Gnetales: Siphonospermum simplexgen. et sp. nov. from the Yixian Formation of Northeast China|url= |journal=BMC Evolutionary Biology|volume=10|issue=1|pages=183|doi=10.1186/1471-2148-10-183|issn=1471-2148|pmc=2900273|pmid=20565755 |doi-access=free |bibcode=2010BMCEE..10..183R }}</ref> Yixian Formation, China, Early Cretaceous (Aptian)
*''[[Welwitschiophyllum]]'' Dilcher et al., 2005 Crato Formation, Brazil, Early Cretaceous (Aptian), [[Akrabou Formation]], Morocco, Late Cretaceous ([[Cenomanian]]-[[Turonian]]) (Initially interpreted as a member of Welwitschiaceae, later considered uncertain).<ref>{{Cite journal|last1=Roberts|first1=Emily A.|last2=Martill|first2=David M.|last3=Loveridge|first3=Robert F.|date=February 2020|title=Phytogeographical implications of the probable occurrence of the gnetalean plant Welwitschiophyllum in the Late Cretaceous (Cenomanian) of Africa|journal=Proceedings of the Geologists' Association|language=en|volume=131|issue=1|pages=1–7|doi=10.1016/j.pgeola.2019.10.002|bibcode=2020PrGA..131....1R |doi-access=free}}</ref><ref>{{Cite journal|last1=Roberts|first1=Emily A.|last2=Loveridge|first2=Robert F.|last3=Weiß|first3=Jörg|last4=Martill|first4=David M.|last5=Seyfullah|first5=Leyla J.|date=August 2020|title=Reinvestigating the fossil leaf Welwitschiophyllum brasiliense Dilcher et al. (2005), from the Lower Cretaceous Crato Formation of Brazil|url=https://linkinghub.elsevier.com/retrieve/pii/S0195667119303684|journal=Cretaceous Research|language=en|volume=112|pages=104471|doi=10.1016/j.cretres.2020.104471|bibcode=2020CrRes.11204471R |s2cid=216313064}}</ref>
*''[[Dayvaultia]]'' Manchester et al. 2021<ref>{{Cite journal|last1=Manchester|first1=Steven R.|last2=Zhang|first2=Xiaoqing|last3=Hotton|first3=Carol L.|last4=Wing|first4=Scott L.|last5=Crane|first5=Peter R.|date=2021-05-19|title=Distinctive quadrangular seed-bearing structures of gnetalean affinity from the Late Jurassic Morrison Formation of Utah, USA|url=https://doi.org/10.1080/14772019.2021.1968522|journal=Journal of Systematic Palaeontology|volume=19|issue=10|pages=743–760|doi=10.1080/14772019.2021.1968522|bibcode=2021JSPal..19..743M |s2cid=239021014|issn=1477-2019|url-access=subscription}}</ref> [[Morrison Formation]], USA, Late Jurassic ([[Tithonian]])
*''[[Daohugoucladus]]'' Yang et al. 2023<ref>{{Cite journal |last1=Yang |first1=Yong |last2=Yang |first2=Zhi |last3=Lin |first3=Longbiao |last4=Wang |first4=Yingwei |last5=Ferguson |first5=David Kay |date=January 2023 |title=A New Gnetalean Macrofossil from the Mid-Jurassic Daohugou Formation |journal=Plants |language=en |volume=12 |issue=9 |pages=1749 |doi=10.3390/plants12091749 |pmid=37176807 |pmc=10181303 |issn=2223-7747 |doi-access=free }}</ref> [[Daohugou Bed]], China, Middle Jurassic ([[Callovian]])
Possible gnetophytes (not confirmed as members of the group)
*''[[Archaestrobilus]]'' [[Trujillo Formation]], Texas, United States, Upper Triassic
*''[[Dechellyia]]''-''[[Masculostrobus]]'' Mongolia, Early Cretaceous (Aptian-Albian)
*''[[Dinophyton]]'' [[Chinle Formation]], United States, Upper Triassic
*''[[Nataligma]]'' [[Molteno Formation]], South Africa, Upper Triassic (Carnian)
*''[[Palaeognetaleana]]'' Wang, 2004,<ref name="Zi-Qiang Wang-2004" /> China, Upper Permian
*''[[Sanmiguelia]]'' United States, Late Triassic-Early Jurassic
*''[[Eoantha]]'' Russia, Early Cretaceous
*''[[Bassitheca]]'' Morrison Formation, USA, Late Jurassic (Tithonian)

==References==
{{reflist|25em}}

'''Other Sources:'''
{{commons category|Gnetophyta}}
*{{cite book
 |last1=Gifford |first1=Ernest M.
 |last2=Foster  |first2=Adriance S.
 |year=1989
 |title=Morphology and Evolution of Vascular Plants
 |edition=Third
 |publisher=W.H. Freeman and Company
 |place=New York, NY
}}
*{{cite journal
 |last1=Hilton  |first1=Jason 
 |last2=Bateman |first2=Richard M.
 |year=2006
 |title=Pteridosperms are the backbone of seed-plant phylogeny
 |journal=Journal of the Torrey Botanical Society
 |volume=133  |pages=119–168
 |doi=10.3159/1095-5674(2006)133[119:PATBOS]2.0.CO;2 
 |s2cid=86395036 
 |url=http://www.bioone.org/perlserv/?request=get-abstract&doi=10.3159%2F1095-5674(2006)133%5B119%3APATBOS%5D2.0.CO%3B2&ct=1
|url-access=subscription}}

{{Plant classification}}
{{Life on Earth}}
{{Taxonbar|from1=Q309147|from2=Q1011212}}

[[Category:Gnetophyta| ]]
[[Category:Plant divisions]]
[[Category:Extant Permian first appearances]]