Progymnosperm
The progymnosperms are an extinct group of woody, spore-bearing plants that is presumed to have evolved from the trimerophytes, and eventually gave rise to the gymnosperms, ancestral to acrogymnosperms and angiosperms (flowering plants). They have been treated formally at the rank of division Progymnospermophyta or class Progymnospermopsida (as opposite). The stratigraphically oldest known examples belong to the Middle Devonian order the Aneurophytales, with forms such as "Protopteridium", in which the vegetative organs consisted of relatively loose clusters of axes. "Tetraxylopteris" is another example of a genus lacking leaves. In more advanced aneurophytaleans such as "Aneurophyton" these vegetative organs  started to look rather more like fronds, and eventually during Late Devonian times the aneurophytaleans are presumed to have given rise to the pteridosperm order, the Lyginopteridales. In Late Devonian times, another group of progymnosperms gave rise to the first really large trees known as "Archaeopteris". The latest surviving group of progymnosperms is the Noeggerathiales, which persisted until the end of the Permian. Other characteristics: Phylogeny. Progymnosperms are a paraphyletic grade of plants.