Plants herbaceous, annual or perennial, with milky sap, glabrous to stellate-pubescent, submersed, floating leaves, or emergent in fresh or brackish waters. Roots fibrous, few to many, septate or aseptate, at base or lower nodes of stem. Stems corm-like, rhizomatous, or stoloniferous, rhizomes occasionally terminated by tubers. Leaves basal, sessile or petiolate; petioles terete to triangular, mostly 2 or more times length of blade, with sheathing base; blades linear, elliptic, ovate to rhomboid, with or without pellucid markings of dots or lines, margin entire or undulate, apex obtuse, acute, or acuminate, base with or without basal lobes, if without basal lobes, then attenuate, if with basal lobes, then truncate, cordate, sagittate, or hastate, venation reticulate, with parallel primary veins from base of blade to apex and reticulate secondary veins. Inflorescences scapose, mostly erect, rarely floating or decumbent, verticillate, forming racemes or verticils branching to become paniculate, rarely umbellate, without a subtending spathe, bracteolate; bracts whorled, linear, delicate to coarse, smooth to papillose, entire, obtuse to acute. Flowers hypogynous, bisexual or unisexual (plants monoecious, rarely dioecious), subsessile to long pedicellate; perianth actinomorphic, of 6 free segments in 2 series, sepals 3, green, persistent, erect and enclosing flower and fruit or spreading to reflexed, petals 3, delicate, larger than sepals, deciduous; stamens absent or of 6 to many, separate, anthers 2-locular, elongate, basifixed or versatile, dehiscing by longitudinal slits; pollen 5-aperturate, globose, separate; gynoecium absent or of 6 to many separate carpels, spirally arranged, carpels 1-locular, each with 1 or rarely 2 anatropous ovules, placentation basal, styles terminal or lateral, persistent, stigmas linear. Achenes compressed or terete, mostly numerous, often winged, longitudinally ribbed or not ribbed, glandular or eglandular; seeds 1-few, U-shaped; endosperm helobial or nuclear in development, absent in mature seeds.