Pteridosperms
The term Pteridospermatophyta (or "seed ferns" or "Pteridospermatopsida") is a polyphyletic group of extinct seed-bearing plants (spermatophytes). The earliest fossil evidence for plants of this type is the genus ''Elkinsia'' of the late Devonian age. 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. With regard to the enduring utility of this 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 v ...
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Lyginopteridales
The Lyginopteridales were the archetypal pteridosperms: They were the first plant fossils to be described as pteridosperms and, thus, the group on which the concept of pteridosperms was first developed;Oliver, F. W. & Scott, D. H. (1904). "On the structure of the Palaeozoic seed ''Lagenostoma Lomaxi'', with a statement of the evidence upon which it is referred to ''Lyginodendron''." ''Philosophical Transactions of the Royal Society of London, Series B,'' 197: 193-247. they are the stratigraphically oldest-known pteridosperms, occurring first in late Devonian strata;Rothwell, G. W., Scheckler, S. E. & Gillespie, W. H. (1989). "''Elkinsia'' gen. nov., a Late Devonian gymnosperm with cupulate ovules." ''Botanical Gazette,'' 150: 170-189. and they have the most primitive features, most notably in the structure of their ovules.Long, A. G. (1959). "On the structure of ''Calymmatotheca kidstoni'' Calder (emended) and ''Genomosperma latens'' gen. et sp. nov. from the Calciferous Sandst ...
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