Filmy Ferns

Small epiphytic or terrestrial ferns mostly found in rainforests under very moist conditions. Rhizome long-creeping or short and thick, often slender or filiform, clothed with hairs, sometimes without roots. Stipes unwinged or frequently winged almost to the base, mostly filiform or slender, glabrous or hairy. Lamina simple or bifid or palmatifid or 1-pinnate to pinnately decompound, usually one cell in thickness except the veins, membranous, almost transparent, lacking stomates. Pinnae with plain or pitted walls, glabrous or clothed with simple to elaborately branched hairs. Ultimate segments small, mostly 1-veined. Veins free except in a few cases. Sori marginal, terminal on the pinnules or on short lateral lobes. Involucre (indusium) bivalvate tubular or obconic; the lips often much distended. Receptacle columnar, included to long-exserted. Sporangia spherical to compressed, very shortly stalked or sessile, clustered along the receptacle, basipetal or maturing at the same time; the annulus complete, oblique or almost transverse, opening by a ± longitudinal slit. Spores tetrahedral or globoso-tetrahedral, without a perispore.