General characteristic features of Pteridophytes

In pteridophytes the sporophyte (2n) is the dominant, long-lived, independent phase, and it is differentiated into true root, stem and leaves — a real step up from the bryophyte body plan. Roots are adventitious, and the stem branches monopodially or dichotomously. Leaves may be small and single-veined (microphyllous) or larger and more elaborately veined (megaphyllous). The internal vascular cylinder (stele) is usually a protostele, though some genera (e.g. Marsilea) have a siphonostele; tracheids are the main water-conducting cells, though Selaginella additionally has true vessels.

Spore-bearing structures called sporangia are borne on special leaves called sporophylls, which are often organised into a cone or strobilus (e.g. Selaginella, Equisetum). Pteridophytes may be homosporous (one spore type, e.g. Lycopodium) or heterosporous (two spore types, e.g. Selaginella) — and heterospory is regarded as the evolutionary origin of the seed habit. Sporangium development is either eusporangiate (arising from a group of initial cells) or leptosporangiate (arising from a single initial cell). Spore mother cells undergo meiosis to produce haploid spores, which germinate into a small, multicellular, green, heart-shaped, independent gametophyte called the prothallus. Vegetative reproduction can occur via fragmentation, resting buds, root tubers and adventitious buds. …