Gnetophyta

Gnetophyta Temporal range: Jurassic–recent PreꞒ Ꞓ O S D C P T J K Pg N
Welwitschia mirabilis female plant with cones
Scientific classification
Kingdom:	Plantae
Clade:	Tracheophytes
Clade:	Gymnospermae
Division:	Gnetophyta Bessey 1907
Class:	Gnetopsida Thom 1886
Families and genera
Gnetaceae   Gnetum Welwitschiaceae   Welwitschia Ephedraceae    Ephedra
Distribution, separated by genus: Green – Welwitschia Blue – Gnetum Red – Ephedra Purple – Gnetum and Ephedra

Gnetophyta (

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 (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.^{[1][2][3][4][5]}

Ecology and morphology

Unlike most biological groupings, it is difficult to find many common characteristics between all of the members of the gnetophytes.

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

Recent research by Lee, Cibrian-Jaramillo, et al. (2011) suggests that the Gnetophyta are a sister group to the rest of the gymnosperms,[13] 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

From the early twentieth century, the anthophyte hypothesis was the prevailing explanation for seed plant evolution, based on shared 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".^[7] 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.^{[7][21][22][23]} However, most genetic studies, as well as more recent morphological analyses,^[24] have rejected the anthophyte hypothesis.^{[2][14][15][18][19][25][26][27][28][29][excessive citations]}

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.^[2][7][25]

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.^[7] According to this hypothesis, the conifers as currently defined are not a monophyletic group, in contrast with molecular findings that support its monophyly.^[16] All existing evidence for this hypothesis comes from molecular studies since 1999.^{[2][3][25][27][18][15][19][20][30][31]} A 2018 phylogenomic study estimated the divergence between Gnetales and Pinaceae at around 241 millions of years ago, in the early Triassic^[30] while a 2021 study placed it earlier, in the Carboniferous.^[31]

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),

Some partitions of the genetic data suggest that the gnetophytes are sister to all of the other extant seed plant groups.[4]^{[7][18][19][16][32][33]} However, there is no morphological evidence nor examples from the fossil record to support the gnetophyte-sister hypotheses.^[20]

Fossil gnetophytes

Knowledge of gnetophyte history through fossil discovery has increased greatly since the 1980s.^[1] Although some fossils that have been proposed to be gnetophytes have been found as far back as the Permian,^[34] their affinites to the group are equivocal. The oldest fossils that are definitely assignable to the group date to the Late Jurassic.^[35] Overall, the fossil record of the group is richest during the Early Cretaceous, exhibiting a substantial decline during the Late Cretaceous.^[35]

Ephedraceae

• Leongathia V.A. Krassilov, D.L. Dilcher & J.G. Douglas 1998^[36] Koonwarra fossil bed, Australia, Early Cretaceous (Aptian)
• Jianchangia Yang, Wang and Ferguson, 2020^[37] Jiufotang Formation, China, Early Cretaceous (Aptian)
• Eamesia Yang, Lin and Ferguson, 2018^[38] Yixian Formation, China, Early Cretaceous (Aptian)
• Prognetella Krassilov et Bugdaeva, 1999 Yixian Formation, China, Early Cretaceous (Aptian) (initially interpreted as an angiosperm)^[39]
• Chengia Yang, Lin & Wang, 2013,^[40] Yixian Formation, China, Early Cretaceous (Aptian)
• 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^[41] China, Early Cretaceous

Gnetaceae

• Khitania Guo et al. 2009^[42] 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).^[43]
• Drewria Crane & Upchurch, 1987 Potomac Group, USA, Albian (possible affinities to Welwitschiaceae)^[44]
• Bicatia Friis, Pedersen and Crane, 2014^[44] Figueira da Foz Formation, Portugal, Early Cretaceous (late Aptian early Albian), Potomac Group, USA, Albian (possible affinities to Welwitschiaceae)
• Liaoningia Yang et al, 2017^[45] Yixian Formation, China, Early Cretaceous (Aptian)
• Daohugou Bed, China, Middle Jurassic (Callovian
  )
• Itajuba Ricardi-Branco et al, 2013,^[47] Crato Formation, Brazil, Early Cretaceous (Aptian)
• Protoephedrites Rothwell et Stockey, 2013^[48] Canada, Valanginian (possible ephedroid affinities)
• Siphonospermum Rydin et Friis, 2010^[49] 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).^[50][51]
• Dayvaultia Manchester et al. 2021^[52] Morrison Formation, USA, Late Jurassic (Tithonian)
• 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,^[34] China, Upper Permian
• Sanmiguelia United States, Late Triassic-Early Jurassic
• Eoantha Russia, Early Cretaceous
• Bassitheca Morrison Formation, USA, Late Jurassic (Tithonian)

References

1. ^
   PMID 21652317
   .
2. ^
   PMID 10760278
   .
3. ^
   PMID 11697913
   .
4. ^
   doi:10.1139/B08-062
   .
5. S2CID 55148071
   .
6. doi:10.1093/oxfordjournals.aob.a089185
   .
7. ^ ^{a b c d e f g} 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.
8. ^ 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.
9. ^ Pearson, H.H.W. (2010) [1929]. Gnetales. Cambridge University Press.
   ISBN 978-1108013987
   .
10. ^ Lawrence, George Hill Mathewson. Taxonomy of vascular plants. Macmillan, 1951
11. ^ Foster, Adriance S.; Gifford, Ernest M. Jr. (1974). Comparative Morphology of Vascular Plants. Freeman.
    ISBN 0-7167-0712-8
    .
12. ^ Friis, Else Marie; Crane, Peter R.; Pedersen, Kaj Raunsgaard; Bengtson, Stefan; Donoghue, Philip C.J.; Grimm, Guido W.; Stampanoni, Marco (November 2007). "Phase-contrast X-ray microtomography links Cretaceous seeds with Gnetales and Bennettitales". Nature. 450 (7169): 549–552.
    S2CID 1198220
    .
13. ^ Lee, E.K.; Cibrian-Jaramillo, A.; Kolokotronis, S.O.; Katari, M.S.; Stamatakis, A.; et al. (2011). "A functional phylogenomic view of the seed plants". PLOS Genet. 7 (12): e1002411.
    PMID 22194700
    .
14. ^ ^{a b} Chaw, S.M.; Aharkikh, A.; Sung, H.M.; Lau, T.C.; Li, W.H. (1997). "Molecular phylogeny of extant gymnosperms and seed plant evolution: Analysis of nuclear 18S rRNA sequences". Molecular Biology and Evolution. 14 (1): 56–68.
    PMID 9000754
    .
15. ^ ^{a b c} Qiu, Y.L.; Lee, J.; Bernasconi-Quadroni, F.; Soltis, D.E.; Soltis, P.S.; Zanis, M.; Zimmer, E.A.; Chen, Z.; Savalainen, V. & Chase, M.W. (1999). "The earliest angiosperms: evidence from mitochondrial, plastid and nuclear genomes". Nature. 402 (6760): 404–407.
    S2CID 4380796
    .
16. ^ ^{a b c} Rydin, C.; Kallersjo, M.; Friist, E.M. (2002). "Seed plant relationships and the systematic position of Gnetales based on nuclear and chloroplast DNA: Conflicting data, rooting problems, and the monophyly of conifers". International Journal of Plant Sciences. 163 (2): 197–214.
    S2CID 84578578
    .
17. ^ Braukmann, T.W.A.; Kuzmina, M.; Stefanovic, S. (2009). "Loss of all plastid nhd genes in Gnetales and conifers: Extent and evolutionary significance for the seed plant phylogeny". Current Genetics. 55 (3): 323–337.
    S2CID 3939394
    .
18. ^ ^{a b c d e} Magallon, S.; Sanderson, M.J. (2002). "Relationships among seed plants inferred from highly conserved genes: sorting conflicting phylogenetic signals among ancient lineages". American Journal of Botany. 89 (12): 1991–2006.
    PMID 21665628
    .
19. ^ ^{a b c d} Sanderson, M.J.; Wojciechowski, M.F.; Hu, J.M.; Sher Khan, T.; Brady, S.G. (2000). "Error, bias, and long-branch attraction in data for two chloroplast photosystem genes in seed plants". Molecular Biology and Evolution. 17 (5): 782–797.
    PMID 10779539
    .
20. ^ ^{a b c} Burleigh, J.G.; Mathews, S. (2007). "Phylogenetic signal in nucleotide data from seed plants: Implications for resolving the seed plant tree of life". American Journal of Botany. 168 (10): 125–135.
    PMID 21652311
    .
21. ^ Donoghue, M.J.; Doyle, J.A. (2000). "Seed plant phylogeny: demise of the anthophyte hypothesis?". Current Biology. 10 (3): R106–R109.
    S2CID 16558206
    .
22. ^ Loconte, H.; Stevenson, D.W. (1990). "Cladistics of the Spermatophyta". Brittonia. 42 (3): 197–211.
    S2CID 36908568
    .
23. ^ Nixon, K.C.; Crepet, W.L.; Stevenson, D.; Friis, E.M. (1994). "A reevaluation of seed plant phylogeny". Annals of the Missouri Botanical Garden. 81 (3): 494–533.
    JSTOR 2399901
    .
24. ^ Coiro, M.; Chomicki, G.; Doyle, J.A. (2018). "Experimental signal dissection and method sensitivity analyses reaffirm the potential of fossils and morphology in the resolution of the relationship of angiosperms and Gnetales". Paleobiology. 44 (3): 490–510.
    S2CID 91488394
    .
25. ^ ^{a b c d} Chaw, S.M.; Parkinson, C.L.; Cheng, Y.; Vincent, T.M.; Palmer, J.D. (2000). "Seed plant phylogeny inferred from all three plant genomes: Monophyly of extant gymnosperms and origin of Gnetales from conifers". Proceedings of the National Academy of Sciences USA. 97 (8): 4086–4091.
    PMID 10760277
    .
26. ^ Goremykin, V.; Bobrova, V.; Pahnke, J.; Troitsky, A.; Antonov, A.; Martin, W. (1996). "Noncoding sequences from the slowly evolving chloroplast inverted repeat in addition to rbcL data do not support gnetalean affinities of angiosperms". Molecular Biology and Evolution. 13 (2): 383–396.
    PMID 8587503
    .
27. ^ ^{a b} Hajibabaei, M.; Xia, J.; Drouin, G. (2006). "Seed plant phylogeny: Gnetophytes are derived conifers and a sister group to Pinaceae". Molecular Phylogenetics and Evolution. 40 (1): 208–217.
    PMID 16621615
    .
28. ^ Hansen, A.; Hansmann, S.; Samigullin, T.; Antonov, A.; Martin, W. (1999). "Gnetum and the angiosperms: molecular evidence that their shared morphological characters are convergent rather than homologous". Molecular Biology and Evolution. 16 (7): 1006–1009.
    doi:10.1093/oxfordjournals.molbev.a026176
    .
29. ^ Samigullin, T.K.; Martin, W.F.; Troitsky, A.V.; Antonov, A.S. (1999). "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 of Molecular Evolution. 49 (3): 310–315.
    S2CID 4232968
    .
30. ^
    PMID 29925623
    .
31. ^
    S2CID 236141481
    .
32. ^ Zhang, Y; Liu, Z. (7 May 2019). "Genic evidence that gnetophytes are sister to all other seed plants". bioRxiv (preprint). Cold Springs Harbor Laboratory.
    doi:10.1101/629915
    . bioRxiv 629915.
33. ^ Chen, Z.-D.; Yang, T.; Lin, L.; Lu, L.-M.; Li, H.-L.; Sun, M.; et al. (2016). "Tree of life for the genera of Chinese vascular plants". Journal of Systematics and Evolution. 54 (4): 277–306.
    doi:10.1111/jse.12219
    .
34. ^
    PMID 15229124
    .
35. ^
    ISSN 2296-701X
    .
36. ISSN 0311-5518
    .
37. PMID 32019502
    .
38. PMID 30157769
    .
39. doi:10.1016/j.ppees.2015.06.006
    .
40. PMID 23530702
    .
41. doi:10.1016/j.pld.2024.03.002
    .
42. hdl:2027.42/74128
    .
43. ^ Brea, Mariana; Silvia, Gnaedinger; Martínez, Leandro C.A. (2023). "Archangelskyoxylon carlquistii gen. et sp. nov. Taxonomy and phylogeny of an unequivocal gnetoid Jurassic fossil wood". Review of Palaeobotany and Palynology (105035). Retrieved 29 November 2023.
44. ^
    ISSN 0017-3134
    .
45. doi:10.1016/j.cretres.2017.02.007
    .
46. doi:10.1016/j.ppees.2017.08.001
    .
47. ISBN 978-953-51-1132-0
    , retrieved 2020-12-05
48. S2CID 84063572
    .
49. PMID 20565755
    .
50. doi:10.1016/j.pgeola.2019.10.002
    .
51. S2CID 216313064
    .
52. S2CID 239021014
    .
53. PMID 37176807
    .

Other Sources:

Wikimedia Commons has media related to Gnetophyta.

• Gifford, Ernest M.; Foster, Adriance S. (1989). Morphology and Evolution of Vascular Plants (Third ed.). New York, NY: W.H. Freeman and Company.
• Hilton, Jason; Bateman, Richard M. (2006). "Pteridosperms are the backbone of seed-plant phylogeny". Journal of the Torrey Botanical Society. 133: 119–168.
  S2CID 86395036
  .