Herbs, 0.5--30(--50) cm. Leaves submersed, floating, or emersed; submersed sessile, ribbonlike; floating linear, 15--100 ´ 0.2--2(--3) cm, blade present or absent; emersed petiolate, rarely sessile, blade linear-lanceolate, lanceolate, or narrowly elliptic, 4--2--6 ´ 1.5 cm. Inflorescences to 50 cm. Flowers cleistogamous in submersed plants, chasmogamous in terrestrial; sepals 1.5--3 mm; petals faint purplish white, 2--4 mm, margin entire to slightly erose, apex obtuse; anthers ovoid, 0.3--0.6 mm; style ± coiled, 0.4--0.5 mm, ½ length ovary. Fruiting heads 3--6 mm diam.; achenes orbicular to orbicular-ovoid, 2--2.7 mm, with 2 shallow, abaxial grooves lateral to 1 abaxial ridge, beak erect. 2n =14. Flowering summer--fall. Shallow fresh or brackish water or muddy shores; 30--1800 m; Alta., B.C., Man., Ont., Que., Sask.; Ariz., Calif., Colo., Idaho, Minn., Mont., Nebr., Nev., N.Y., N.Dak., Oreg., S.Dak., Utah, Vt., Wash., Wyo.; Eurasia; n Africa.