Plants epiphytic, terrestrial, or on rock. Stems long-creeping,
often threadlike and intertwining, or short-erect, protostelic,
bearing brown hairs of 1--2 types. Roots sparse or absent.
Leaves small, 0.5--20 × 0.2--5 cm, often forming dense mats.
Petiole short, threadlike to wiry, often winged part or entire
length. Blade ovate or oblong to lanceolate, simple to
decompound, usually 1 cell thick between veins (except
Trichomanes membranaceum Linnaeus), entire or dentate; scales or
simple and/or stellate hairs often borne on veins or leaf
margins. Veins free and divergent, occasionally present as
unattached 'false' veins. Sori marginal on vein ends, enclosed
by 2-valved or conic involucres. Sporangia borne on moundlike
receptacle or on elongate 'bristle,' sessile or short-stalked;
annulus oblique. Spores green, globose, trilete. Gametophytes
filamentous or ribbonlike or a combination of both, much
branched, 0.2--1 cm, often bearing gemmae, persistent, clone-
forming by vegetative reproduction. Species outside t