FILMY FERNS, a general name for a family of ferns, the Hymenophyllaceae, with delicate, much-divided leaves and often moss-like growth, comprising the genera Hymenophyllum and Tricliomanes, together comprising some 450 species, natives chiefly of the humid tropics and mainly epiphytic. Two species of Trichomanes occur in the south-eastern United States. Various species are in greenhouse cultivation. They require to be kept in close cases in a cool fernery, and the stones and moss amongst which they are grown must be kept continually moist so that the evaporated water condenses on the leaves.