| Noun | 1. | class Pteridospermopsida - extinct gymnosperms most of Carboniferous to Jurassic: seed ferns and allies class - (biology) a taxonomic group containing one or more orders class Gymnospermae, division Gymnospermophyta, Gymnospermae, Gymnospermophyta - plants having naked seeds not enclosed in an ovary; in some systems considered a class (Gymnospermae) and in others a division (Gymnospermophyta); comprises three subdivisions (or classes): Cycadophytina (class Cycadopsida) and Gnetophytina (class Gnetopsida) and Coniferophytina (class Coniferopsida); in some classifications the Coniferophytina are divided into three groups: Pinophytina (class Pinopsida) and Ginkgophytina (class Ginkgopsida) and Taxophytina (class Taxopsida) Cycadofilicales, Lyginopteridales, order Cycadofilicales, order Lyginopteridales - fossil gymnospermous trees or climbing plants from the Devonian: seed ferns |