A recently discovered fossil group, the Pteridospermae have characters intermediate between the Ptendophyta and the more primitive seedplants.
The subject of palaeontological botany has been advanced by the researches of both botanists and geologists.
In recent years the science of vegetable palaeontology has been given the distinct name of Palaeobotany, so that " palaeontology e' among biologists mainly refers to zoology; but historically the two cannot be disconnected.
In the meantime the foundations of palaeobotany were being laid (1804) by Ernst Friedrich von Schlotheim (1764-1832), (1811) by Kaspar Maria Sternberg (1761-1838) and (1838) by Theophile Brongniart (1801-1876).
His activity was by no means confined to palaeobotany, but extended into all branches of botany, more particularly anatomy and phanerogamic taxonomy.
These plants, a fuller description of which must be sought in the article Palaeobotany: Palaeozoic, underwent secondary increase in thickness and attained the size of large trees; the aerial stem was more or less branched dichotomously.
In the absence of direct evidence from Palaeobotany, and bearing in mind the modifications associated with adaptation to an aquatic life in other plants, the recognition of any more definite affinity for these heterosporous ferns than that indicated above appears to be inadvisable.