Progymnosperms Progymnosperms, as the name implies, are plants that share important derived features with seed plants but are still free-sporing themselves. However, they were spore-bearing. Branching in Tetraxylopteris is decussate , meaning that pairs of branches emerge together on opposite sides of the main axis, with pairs above and below arranged at right angles to the pair between. In sterile axes, terminal branches have been interpreted as leaves. Fertile branch with sporangia on pinnate ultimate branches.
Fertile branches arise in place of the leaf-like branch systems.
Sporangia open laterally, a primitive feature retained from Pertica and Psilophyton -grade ancestors. However, Tetraxylopteris appears to have a zone of specialized cells to facilitate sporangial dehiscence. Tetraxylopteris was homosporous also like earlier euphyllophytes. Aneurophyton is also known from the Middle and Late Devonian. Aneurophyton is similar to Tetraxylopteris in overall form, but its branches are arranged helically rather than decussately.