Aquatic or subaquatic perennials. Rhizome long, slender, creeping, hairy. Leaves radical or some of them cauline, circinnate in bud, simple, filiform-linear and without blade or with blade of 2 or 4 leaflets palmately arranged on a long petiole; veins dichotomous. Sporangia borne in leathery or membranous, globular or ovoid-oblong, 1- or many-celled sporocarps dehiscent at maturity, each sporocarp containing 1 or more sori surrounded by an indusium; sorus mostly consisting of macro- and micro-sporangia; macrosporangium with 1 macrospore, microsporangium with numerous small microspores; annulus rudimentary or 0.