Psilophytopsida is a now obsolete class containing one order, Psilophytales, which was previously used to classify a number of extinct plants which are now placed elsewhere.
The class was established in 1917, under the name Psilophyta, with only three genera (Rhynia, Horneophyton and Psilophyton)[1] for a group of fossil plants from the Upper Silurian and Devonian periods which lack true roots and leaves, but have a vascular system within a branching cylindrical stem.
All lacked leaves and true roots, consisting only of branched stems; however they were considered to contain vascular tissue.
As described by Sporne in 1966, Psilophytopsida consisted of four families:[5] By 1975, it had become clear that the class had become increasingly unnatural, containing unrelated early vascular plants.
Separating out 'basal groups', such as the earliest land plants, is intrinsically difficult, since at this stage they contain many shared characters (plesiomorphies) which are not sufficient to distinguish them.