Herbs, annual or perennial, not stranded by low tide. Leaves submersed and emersed; submersed leaves sessile, blade linear; emersed leaves petiolate, blade hastate to sagittate. Inflorescences of 1--15 whorls, floating or emersed; bracts distinct. Flowers: pistillate with ring of sterile stamens; petals without purple spot at base. Flowering mid summer--fall. Mud flats of lakes and rivers; 5--2000 m; Ala., Ark., Calif., Colo., Del., Ga., Ill., Ind., Iowa, Kans., Ky., La., Mich., Minn., Miss., Mo., Nebr., N.Mex., N.C., Ohio, Okla., S.C., S.Dak., Tenn., Tex., Va., W.Va., Wis. ; Mexico (Chihuahua, Coahuila, Sinaloa).