With regard to the enduring utility of thisdivision, many palaeobotanists still use the pteridosperm grouping in an informal sense to refer to the seed plants that are notangiosperms,coniferoids (conifers orcordaites),ginkgophytes (ginkgos orczekanowskiales),cycadophytes (cycads orbennettites), orgnetophytes. This is particularly useful for extinct seed plant groups whose systematic relationships remain speculative, as they can be classified as pteridosperms with no invalid 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.
The concept of pteridosperms goes back to the late 19th century whenpalaeobotanists came to realise that many Carboniferous fossils resembling fern fronds had anatomical features more reminiscent of the modern-day seed plants, thecycads. In 1899 the German palaeobotanistHenry Potonié coined the term "Cycadofilices" ("cycad-ferns") for such fossils, suggesting that they were a group of non-seed plants intermediate between theferns and cycads.[4] Shortly afterwards, the British palaeobotanistsFrank Oliver andDukinfield Henry Scott (with the assistance of Oliver's student at the time,Marie Stopes) made the critical discovery that some of these fronds (genusLyginopteris) were associated with seeds (genusLagenostoma) that had identical and very distinctive glandular hairs, and concluded that both fronds and seeds belonged to the same plant.[5] Soon, additional evidence came to light suggesting that seeds were also attached to the Carboniferous fern-like frondsDicksonites,[6]Neuropteris[7] andAneimites.[8] 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 andPeltaspermales, with "Mesozoic seed ferns" including thePetriellales,Corystospermales andCaytoniales.[9]
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.[citation needed]
During the 20th century the concept of pteridosperms was expanded to include various Mesozoic groups of seed plants with fern-like fronds, such as theCorystospermaceae. Some palaeobotanists also included seed plant groups with entire leaves such as theGlossopteridales andGigantopteridales, which was stretching the concept. In the context of modern phylogenetic models,[10] 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 aparaphyletic 'grade-group' with no common lineage.[clarification needed] One of the few characters that may unify the group is that theovules were borne in acupule, a group of enclosing branches, but this has not been confirmed for all "pteridosperm" groups.[citation needed]
It has been speculated that some seed fern groups may be close to the ancestry offlowering plants (angiosperms). A 2009 study concluded that "phylogenetic analysis techniques have surpassed the hard data needed to formulate meaningful phylogenetic hypotheses" regarding the relationships of "seed ferns" to living plant groups.[11]
Order †Lyginopteridales(Corsin (1960)) Havlena (1961) [LagenostomatalesSeward ex Long (1975); LyginodendralesNemejc (1968); SphenopteridalesSchimper 1869]
^Rothwell G. W.; Scheckler S. E.; Gillespie W. H. (1989). "Elkinsia gen. nov., a Late Devonian gymnosperm with cupulate ovules".Botanical Gazette.150 (2):170–189.doi:10.1086/337763.S2CID84303226.
^Grand'Eury C (1904). "Sur les graines Neuropteridées".Comptes Rendus de l'Académie des Sciences de Paris.140:782–786.
^Kidston R (1904). "On the fructification ofNeuropteris heterophylla, Brongniart".Philosophical Transactions of the Royal Society of London, Series B.197 (225–238):1–5.doi:10.1098/rstb.1905.0001.
^White D (1904). "The seeds ofAneimites".Smithsonian Institution, Miscellaneous Collection.47:322–331.
^Taylor, Edith L., et al. "Mesozoic Seed Ferns: Old Paradigms, New Discoveries."The Journal of the Torrey Botanical Society, vol. 133, no. 1, 2006, pp. 62–82.JSTOR,JSTOR20063823. Accessed 24 Sept. 2023.
