Herbae aquaticae perennes, parvae. Folia sessilia disticha, simplicia, digitata, 3–8 segmentis, base expansa vaginantia; segmenta in forma et magnitudine variabilia, foliorum juniorum segmento centrali longiori, lineari, cylindrico, interdum apicem versus applanato, flexibili, caduco; segmentis lateralibus 2–3, spiniformibus, induratis, interdum in caulibus veteribus. Flores 1-aliquot per caulem, apicales, hermaphroditi, zygomorphi, pedicellati, per spathellam saccatam tecti; tepala plerumque 3, squamiformia; stamina plerumque 2, libera, ad pistilli latus disposita, caduca; antherae basifixae, introrse longitudinaliterque dehiscentes; pollinis grana in tetradibus, tricolpata; ovarium 2-carpellare, 2-loculare, in gynophoro per anthesin elonganti portatum; stigmata plerumque 2, libera; fructus capsularis, 2-locularis, duabus valvis aequalibus, persistentibus, utraque 3-costata; semina ignota.
Small aquatic perennial herbs, attached to rocks in river-rapids and waterfalls. Roots prostrate, elongate, dorsiventrally flattened, sometimes intertwined, green and photosynthetic, branched, with asymmetric root cap, attached to solid substrata via holdfasts (haptera) and adhesive hairs. Stems arising opposite or subopposite along the flanks of roots, at base becoming broadened and disk-like when older, branched, erect, terete in cross-section at base, sometimes with adventitious roots, monomorphic, dark brown or black. Leaves distichous, upright, monothecous, digitate, with 3 to 8 segments and expanded sheathing base, lacking a central vein, estipulate; segments of the leaf variable in size and form; young leaves with a long central segment, linear, flexible, light green, cylindrical and sometimes flattened on top, caducous, the lateral segments 2–3, shorter than the central segment, flexible to hardened, persistent, filiform, light green, apex acute; older leaves with up to 8 segments, more or less the same size or the central one longer, spine-like, hardened and usually persistent on older stems, black, most internodes between the digitate leaves obscure, leading to crowded leaf arrangement, basal internodes longer and with longitudinal furrows. Flowers 1 to several per stem, apical, achlamydeous, hermaphroditic, zygomorphic, pedicellate, covered by a sac-like spathella (sac-like covering over flower); spathella clavate, smooth, apex rounded, rupturing apically into several irregularly shaped segments, without a cap-like apical segment; tepals usually (2) 3 (4), scale-like, linear or incurved, apex blunt, often darkened distally, alternating with the stamens or sometimes arising from the pedicel; stamens (1) 2 (3), free, on one side of pistil, deciduous; filaments short, elongating during anthesis but never reaching the length of the ovary; anthers basifixed, quadrangular; thecae parallel, apices acute, distinct, of equal heights, dehiscing introrsely and longitudinally; pollen in tetrads, tricolpate; ovary 2-carpellate, 2-locular, globose, with 6 longitudinal dark lines, borne on a gynophore that elongates during anthesis; ovules numerous, placentation axile; stigmas usually 2, rarely 3, free, upright prior to rupture of the spathella, conical when young, divergent and elongating during anthesis; pedicel elongating during anthesis; fruit a capsule, 2-locular, spherical to subellipsoid, with two equal valves (isolobous); valves persistent, each 3 to 7-ribbed, suture margins appearing thickened and rib-like; seeds unknown.