Plants annual or perennial, growing emerged in fresh waters. Roots without septations. Stems rhizomatous. Leaves emerged or submersed; emerged leaves petiolate, petioles mostly triangular, rarely terete, blades linear to broadly ovate, with pellucid markings absent or present as dot or lines; submersed leaves mostly sessile phyllodes, blades mostly linear to rarely ovate, pellucid markings present as dots or lines, or absent. Inflorescences erect, emerged, racemose or paniculate scapes, rarely umbelliform, whorls 1-18; pedicels ascending to recurved. Flowers bisexual, subsessile to pedicellate; sepals herbaceous to coriaceous, without sculpturing, reflexed to spreading or rarely slightly appressed; petals white, larger than sepals; stamens 9 to many, filaments glabrous, anthers versatile or basifixed; gynoecium of many carpels, carpels 1-ovuled, styles terminal or lateral. Achenes terete, often longitudinally ribbed and glandular, rarely with a dorsal keel, separating when mature, beak lateral or terminal, erect, horizontal, or recurved.
Americas, Argentina present, Chile present, Guianas present, Neotropics present, northern U.S.A present
Native to the Americas, consisting of 27 species distributed from northern U.S.A. to Argentina and Chile; 26 species in the Neotropics; 8 species in the Guianas.