Classification of Pteridophytes

Reimer (1954) classified the pteridophytes into five subdivisions spanning 19 orders and 48 families. Psilophytopsida is entirely extinct — its members (e.g. Rhynia) had only a stem and rhizome, with no true roots or leaves, and were homosporous, bearing spore tetrads in terminal sporangia. Psilotopsida (e.g. Psilotum) is rootless and lives in association with fungi; its leaves are reduced to small scaly appendages, the gametophyte is colourless (also fungus-associated), and it is homosporous, with spores produced in sporangia or fused synangia. Lycopsida (e.g. Selaginella, Lycopodium) has true root, stem and leaves, with small, single-veined leaves arranged spirally and bearing a ligule; sporophylls are organised into a strobilus, and the group shows both homospory (Lycopodium) and heterospory (Selaginella). Sphenopsida (e.g. Equisetum) also has true root, stem and leaves, with a jointed stem (distinct nodes and internodes) bearing whorls of small scaly leaves; sporangia sit on peltate discs (sporangiophores) that pack into a compact strobilus, and the group is essentially homosporous, though Equisetum arvense shows incipient heterospory. **Pterop …