Plants terrestrial or epiphytic. Roots numerous. Stems mainly erect, covered with many stiff hairs 1--3 cells long, with simple siphonostele (hollow vascular cylinder). Leaves tufted, monomorphic or dimorphic. Petioles much longer than blades, blades reduced to tiny apical fistlike or radiating groups of rudimentary fertile pinnae ('digits'). Petioles sometimes repeatedly dichotomous, in some species webbed between branches to form fan-shaped false blades. Sporangia arranged in 1--4 ranks on abaxial surface of digits with revolute margins. Annulus subapical, composed of 1--(2--3) layer(s) of thickened cells. Gametophytes subterranean and not green or borne aboveground and green, tuberlike or flattened, cordate or filamentous. Spores bilateral, monolete.