(Benth. & Hook.f.) Engelm. ex J.G.Sm. in N.L.Britton, Man. Fl. N. States, ed. 2: 54 (1905)
Annuals or short-lived perennials, glabrous, scapose, pseudostoloniferous aquatic or semiaquatic plants. Leaves as basal rosette, erect, ascending or floating; emersed leaves petiolate, blades narrow to elliptic, one to three ribbed, with pellucid markings absent or present as lines, the margins entire, the apex acute to acuminate, the base attenuate; submersed leaves sessile phyllodes, the blades linear. Inflorescence erect to creeping, umbelliform or racemose of two to three whorls, vegetatively proliferating or transformed to pseudostolon in submerged conditions, bracts deltoid. Flowers perfect, pedicellate; pedicels spreading in fruit; sepals 3, erect; petals 3, clawed, white, larger than sepals; stamens (6–)9, the anthers short, basifixed, the filaments glabrous; carpels 10–20, separate, each with one ovule. Fruits achenes in a loose head, turgid, obovate, 3–4-ribbed, without keel, without glands, beaked, the beak erect.