Perennial herbs with long, usually creeping stems producing leafless branches (rhizophores) which bear the roots or arise with them on a corm-like swelling at the base of the stem. Leaves small, spirally arranged or 4-ranked and of two kinds, bearing a minute ligule at the base. Heterosporous. Sporangia in leaf axils, the sporangium-bearing leaves in ill- to well-defined cones, with megasporangia at base and microsporangia at apex. Megaspores (1–)4(–42). Microspores numerous. Male gametophyte contained in the microspore until maturity, with a vegetative cell and an antheridium containing numerous biciliate spermatozoids. Female gametophyte many-celled, filling the megaspore and protruding from its split top; archegonia several, at the top of the prothallus. Fertilisation occasionally takes place before the shedding of the megaspore.