Menyanthaceae Dumort.

Annual or perennial aquatic herb, glabrous; stems floating or erect and emergent; rootstock tufted or shortly rhizomatous or stoloniferous. Leaves simple or compound (not in Australia), sometimes dimorphic, alternate, radical or cauline and then leaves often clustered near base of stem, exstipulate; petioles often winged at base and sheathing the stem. Inflorescence a fascicle, panicle, solitary flower or raceme (not in Australia). Flowers actinomorphic, bisexual or unisexual, sometimes heterostylous. Sepals (4 or) 5, free or basally united, persistent. Corolla usually with a short tube, (4 or) 5-lobed, short-lived and deliquescent, white, yellow or pinkish; corolla lobes widely spreading, valvate or induplicate-valvate in bud, usually with entire or fringed side-wings and a transverse fringe of hairs or papillae near the base, sometimes with a papillose or laciniate median keel. Stamens (4 or) 5, alternating with corolla lobes, attached at or near the throat of tube; anthers 2-celled, linear-obloid, longer than filaments, opening introrsely. Gyonecium of 2–5 fused carpels. Ovary superior to inferior, with (4 or) 5 nectary lobes at base, 1-locular, with 2­–5 parietal placentae; style simple, persistent; stigmas 2–5, each with a papillate or laciniate lobe or wing. Fruit a capsule or fleshy berry, globose to ellipsoid, indehiscent or apically 4-valved. Seeds few to many, lenticular to globose, smooth to tuberculate, sometimes winged, endosperm abundant.

Species are sometimes grown as aquatic ornamentals.