Plants perennial, mostly terrestrial, rarely epiphytic, generally in mesic, forested habitats. Stems short- to long-creeping, solenostelic [protostelic], bearing hairs (or less often scales), often branching by means of buds on proximal part of petiole. Leaves monomorphic, circinate in bud. Petiole not articulate, with 1--many vascular bundles, hairy or glabrous [scaly]. Blade 1-pinnate to decompound (rarely simple), glabrous or hairy or with mixture of hairs and glands; rachis and costae grooved adaxially [not grooved in some genera]. Veins free or sometimes joined at margin in fertile segments, pinnate or forking in ultimate segments. Sori near or at blade margin on vein tips or submarginal commissural vein; true (inner) indusia present, free or fused with portion of blade margin to form cup or pouch, or obscured by revolute and usually modified portion of blade margin [indusia rarely absent]; sporangial stalk of 1--3 rows of cells. Spores not green, tetrahedral or bilateral, monolete or trilete. Gametophytes green, cordate, with archegonia and antheridia borne on lower surface. The family is variously circumscribed, in the strict sense including only eight genera, while in the broadest sense encompassing about half the recognized genera of higher ferns (R. E. Holttum 1947). Here it is delimited in the sense of J. T. Mickel (1973). Characteristics that define the family include submarginal or marginal sori with generally two indusia, an inner true indusium and an outer false indusium formed by the revolute, often modified segment margin (although either type may be reduced or absent in some genera); indument usually of hairs rather than scales; and long-creeping protostelic or solenostelic stems with stem buds on the bases of the petioles. Not all genera in the family share all the characteristics.
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