They do not form a monophyletic group but consist of several groups, the Lycopodiophyta (club mosses, spike mosses, and quillworts), the Equisetophyta (horsetails), the Psilotophyta (whisk ferns), the Ophioglossophyta (adder's tongues and grape ferns), and the Pteridophyta (true ferns) and are monocots most of the time.
In addition to these living groups of pteridophytes are several groups now extinct and known only from fossils. These groups include the Rhyniophyta, Zosterophyllophyta, Trimerophytophyta, and the progymnosperms.
Modern studies of the land plants agree that all the pteridophytes share a single common ancestor. However, they are not a clade (monophyletic group) because the seed plants are also descended from within this group -- probably close relatives of the progymnosperms.
These plants are generally sporophyte-oriented; that is, the normal plant is the diploid sporophyte, with the only haploid structure being the gametophyte (prothallium) in season. This basic pattern is like that found in the seed plants but with an important exception. Unlike the seed plants, the pteridophytes have a gametophyte stage that is free-living. As a result, pteridophyte sexuality is more complicated than that of the seed plants. There are several basic categories of sexuality in pteridophytes. The terms distinguish between types of gametophyte sexuality: