Pteridospermatophyta

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Pteridospermatophyta
Temporal range: Carboniferous-Cretaceous (Possible Eocene survival)
FossilFernLeavesPennsylvanianOhio.jpg
Fossil seed fern leaves from the Late Carboniferous of northeastern Ohio.
Scientific classification e
Kingdom: Plantae
Division: Pteridospermatophyta
Orders

The term Pteridospermatophyta (or "seed ferns" or "Pteridospermatopsida") refers to several distinct groups of extinct seed-bearing plants (spermatophytes). The earliest fossil evidence for plants of this type is the genus Elkinsia of the late Devonian age.[1] They flourished particularly during the Carboniferous and Permian periods. Pteridosperms declined during the Mesozoic Era and had mostly disappeared by the end of the Cretaceous Period, though some pteridosperm-like plants seem to have survived into Eocene times, based on fossil finds in Tasmania.[2]

The concept of pteridosperms goes back to the late 19th century when palaeobotanists came to realise that many Carboniferous fossils resembling fern fronds had anatomical features more reminiscent of the modern-day seed plants, the cycads. In 1899 the German palaeobotanist Henry Potonié coined the term "Cycadofilices" ("cycad-ferns") for such fossils, suggesting that they were a group of non-seed plants intermediate between the ferns and cycads.[3] Shortly afterwards, the British palaeobotanists Frank Oliver and Dukinfield Henry Scott (with the assistance of Oliver's student at the time, Marie Stopes) made the critical discovery that some of these fronds (genus Lyginopteris) were associated with seeds (genus Lagenostoma) that had identical and very distinctive glandular hairs, and concluded that both fronds and seeds belonged to the same plant.[4] Soon, additional evidence came to light suggesting that seeds were also attached to the Carboniferous fern-like fronds Dicksonites,[5] Neuropteris[6] and Aneimites.[7] Initially it was still thought that they were "transitional fossils" intermediate between the ferns and cycads, and especially in the English-speaking world they were referred to as "seed ferns" or "pteridosperms". Today, despite being regarded by most palaeobotanists as only distantly related to ferns, these spurious names have nonetheless established themselves. Nowadays, four orders of Palaeozoic seed plants tend to be referred to as pteridosperms: Lyginopteridales, Medullosales, Callistophytales and Peltaspermales.

Their discovery attracted considerable attention at the time, as the pteridosperms were the first extinct group of vascular plants to be identified solely from the fossil record. In the 19th century the Carboniferous Period was often referred to as the "Age of Ferns" but these discoveries during the first decade of the 20th century made it clear that the "Age of Pteridosperms" was perhaps a better description.

During the 20th century the concept of pteridosperms was expanded to include various Mesozoic groups of seed plants with fern-like fronds, such as the Corystospermaceae. Some palaeobotanists also included seed plant groups with entire leaves such as the Glossopteridales and Gigantopteridales, which was stretching the concept. In the context of modern phylogenetic models,[8] the groups often referred to as pteridosperms appear to be liberally spread across a range of clades, and many palaeobotanists today would regard pteridosperms as little more than a paraphyletic 'grade-group' with no common lineage. One of the few characters that may unify the group is that the ovules were borne in a cupule, a group of enclosing branches, but this has not been confirmed for all "pteridosperm" groups.

With regard to the enduring value of the division, many palaeobotanists still use the pteridosperm grouping in an informal sense to refer to the seed plants that are not angiosperms, coniferoids (conifers or cordaites), ginkgophytes or cycadophytes (cycads or bennettites). This is particularly useful for extinct seed plant groups whose systematic relationships remain speculative, as they can be classified as pteridosperms with no valid implications being made as to their systematic affinities. Also, from a purely curatorial perspective the term pteridosperms is a useful shorthand for describing the fern-like fronds that were probably produced by seed plants, which are commonly found in many Palaeozoic and Mesozoic fossil floras.

Phylogeny

An alternative phylogeny of spermatophytes based on the work by Novíkov & Barabaš-Krasni 2015[9] with plant taxon authors from Anderson, Anderson & Cleal 2007[10] showing the relationship of extinct clades.

Spermatophytina

 †Moresnetiopsida Doweld 2001 




 †Lyginopteridopsida Novák 1961 emend. Anderson, Anderson & Cleal 2007 




 †Pachytestopsida Doweld 2001 




 †Callistophytales Rothwell 1981 emend. Anderson, Anderson & Cleal 2007 




 †Peltaspermopsida Doweld 2001 




 †Umkomasiales Doweld 2001 





 †Phasmatocycadopsida Doweld 2001 





 †Pentoxylopsida Pant ex Doweld 2001 



 †Dictyopteridiopsida Doweld 2001


 



 †Cycadeoideopsida Scott 1923 




 †Caytoniopsida Thomas ex Frenguelli 1946 



 Magnoliopsida (Flowering plants)





 

Acrogymnospermae

Cycadopsida (Cycads)




Ginkgoopsida (Maidenhair trees)



Pinopsida (Conifers)











Seed ferns

Taxonomy

References

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  2. Lua error in Module:Citation/CS1/Identifiers at line 47: attempt to index field 'wikibase' (a nil value).
  3. Potonié, H. (1899). Lehrbuch der Pflanzenpaläontologie. Berlin.
  4. Lua error in Module:Citation/CS1/Identifiers at line 47: attempt to index field 'wikibase' (a nil value).
  5. Grand'Eury C (1904). "Sur les graines Neuropteridées". Comptes rendus de l'Académie des Sciences, Paris. 140: 782–786.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  6. Lua error in Module:Citation/CS1/Identifiers at line 47: attempt to index field 'wikibase' (a nil value).
  7. White D (1904). "The seeds of Aneimites". Smithsonian Institution, Miscellaneous Collection. 47: 322–331.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
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  9. Lua error in Module:Citation/CS1/Identifiers at line 47: attempt to index field 'wikibase' (a nil value).
  10. Anderson, Anderson & Cleal (2007). "Brief history of the gymnosperms: classification, biodiversity, phytogeography and ecology". Strelitzia. SANBI. 20: 280. ISBN 978-1-919976-39-6.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>

External links