Low, perennial ferns, mostly terrestrial. Rhizome short, usually vertical, not scaly. Leaves solitary or few, petiolate, not circinnate in bud. Sporophyll reduced to 1 or rarely more, simple or branched stalks, with spikes of 2-rowed sporangia. Sporangia sessile, with walls of several cell layers, without annuli, opening by a slit. Spores numerous, all alike, typically globular-tetrahedral. Prothallium monoecious, usually subterranean, more or less tuberous, usually without chlorophyll but with endotrophic mycorrhiza.
Comprises 3 genera: 2 cosmopolitan, 1 in Tropical Asia and Australasia.