Abstract: The earliest identified seed-plants are found in Latest Devonian aged sediments from Northwest Europe and North America and are believed to have evolved from within the progymnosperms, a group of anatomically advanced pteridophytic plants. However, current evidence makes it problematic to determine from which particular progynmospermous lineage the seed-plants evolved, with the major contender being the Aneurophytalean progymnosperms. The evidence for the ancestral stock to the seed-plants is summarised and the morphologies of the earliest known seed-plants are considered. From their first geological occurrence, the seed-plants are morphologically diverse to such an extent that the identification of a single potential ancestral morphology is impossible. In the light of the evidence so far presented, the precise origin of the seed-plants is unresolved and in need of new evidence relating to the progynmosperm/seed-plant transition. Future lines of research are also suggested.

Key words: Spermatophyte, Lignophyte, Progymnosperm, Evolution, Phylogeny