Perennial herbs with thin, glabrous or hairy, creeping rhizomes. Fronds borne singly along the rhizomes, spirally coiled when young, thin and translucent, of one kind, 1- to 3-pinnate. Sori marginal on the vein endings, often projecting from the lamina. Indusia more or less cup-like, entire or 2-lipped or 2-valved, surrounding the base or the whole of the sorus. Sporangia all alike, shortly stalked, developed successively from apex to base; annulus oblique, without a definite stomium, the sporangia opening laterally by a long slit. Spores 32–420, homosporous. Gametophyte green, surface-living, either filamentous or strap-like.

Contains 34 genera and about 600 species; mostly tropical, a few in moist parts of the temperate zones; absent from dry areas.