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.
Plants epiphytic, petrophilous, or terrestrial, small to medium-sized. Rhizome sometimes short and erect, but usually slender and long creeping, often covered with hairs when young, simple or sometimes irregularly branching. Lamina simple to pinnately decompound, or flabellate, digitate, dichotomous, or even irregularly divided. Segments with a single veinlet, cells in one layer, or rarely with 2-4 cell layers without intercellular spaces and stomata. Sori terminal on veins, solitary, at apex of ultimate segments, or marginal on simple to pinnatifid fronds; involucres cup-shaped to deeply 2-cleft nearly to base; receptacles terminating a vein, short, capitate or clavate, or long and projecting; sporangia shortly stalked to (sub)sessile, maturing basipetally; annulus oblique, not interrupted; dehiscence irregular; spores globose-trilete, tetrahedral, containing chloroplasts, usually short-lived. x = 8, 11, 12, 13, 17, 21, 22, 26, 28, 36, 54 (base numbers x = 8, 54 are doubtful).
Rhizome scaleless, delicate, branching; lvs circinate in bud, the blade only 1 cell thick, lacking stomates, glabrous, with reduced vascular tissue; sori marginal, terminal on the veins, with a valvate or tubular indusium, usually sessile or sunken in the lf-tissue; sporangia borne basipetally on an elongate receptacle, sessile or subsessile, with an oblique complete annulus; spores 32–512; gametophytes monoecious, thalloid or filamentous, long-lived, photosynthetic; small, delicate, chiefly epiphytic ferns. 6/500.
Roots often wanting and replaced by root hairs arising direct from the rhizome or lamina
Delicate herbs with short, erect or slender wide–creeping protostelic rhizomes, with hairs on young parts
Farrar, D. R. 1967. Gametophytes of four tropical fern genera reproducing independently of their sporophytes in the southern Appalachians. Science 155: 1266--1267. Farrar, D. R. 1985. Independent fern gametophytes in the wild. Proc. Roy. Soc. Edinburgh, B 86: 361--369. Morton, C. V. 1968. The genera, subgenera, and sections of the Hymenophyllaceae. Contr. U.S. Natl. Herb. 38: 153--214. Stokey, A. G. 1940. Spore germination and vegetative stages of the gametophytes of Hymenophyllum and Trichomanes. Bot. Gaz. 101: 759--790.
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