1. Hymenophyllum Smith, 5: 418. 1793.
Filmy fern [Greek hymen, membrane, and phyllon, leaf]
Donald R. Farrar
Plants epiphytic or on rock. Stems long-creeping, intertwining, threadlike; hairs brown, sparse. Roots few, delicate. Leaves 1--3-pinnatifid, 2--6 × 0.5--1.5 cm. Petiole short, threadlike, not winged. Blade with inconspicuous glandular hairs or prominent stellate hairs; margins entire to distantly dentate. Soral involucres 2-valved, the halves roundish to ovate. Sporangial receptacle a low mound of tissue included within involucre. Gametophytes persistent, ribbonlike, much branched. Gametophyte gemmae platelike or absent.
Species ca. 310 (3 in the flora): worldwide in tropical regions.
Most species of Hymenophllyum occur in middle elevation rainforests; a few occur in continuously moist temperate habitats. Although all members of this genus are relatively small and delicate, leaves of many species outside the flora become considerably longer by indeterminate growth of the leaf apices.
Taylor, M. S. 1938. Filmy-ferns in South Carolina. J. Elisha Mitchell Sci. Soc. 54: 345--348. Wagner, W. H. Jr., D. R. Farrar, and B. W. McAlpin. 1970. Pteridology of the Highlands Biological Station area, southern Appalachians. J. Elisha Mitchell Sci. Soc. 86: 1--27.