Herbs, annual or perennial, to 50 cm; rhizomes absent; stolons absent; corms present. Leaves submersed, phyllodial, flattened, 4--7 ´ 0.4--0.8 cm, or floating; petiole triangular, to 42 cm; blade sagittate, 3.5--10.5 ´ 1.5--8.5 cm, basal lobes shorter than to equal to length of remainder of blade. Inflorescences racemes, of 1--7 whorls, floating, 0.9--9 ´ 0.6--4 cm; peduncles 10.9--22 cm; bracts distinct or connate less than ¼ total length, broadly lanceolate to linear-lanceolate, 2.8--15 mm, delicate, not papillose; fruiting pedicels spreading to recurved, cylindric, 0.6--2.1 cm. Flowers 1.2--2 cm diam.; sepals spreading in staminate, erect in pistillate, enclosing flower or fruiting head; filaments cylindric, ± equaling anther length, glabrous; pistillate pedicellate, with ring of sterile stamens. Fruiting heads 0.5--1.8 cm diam.; achenes oblanceoloid, abaxially keeled, 1.7--2.2 ´ 1.2--1.5 mm, beaked; faces tuberculate, wings 1--3, ± dentate, glands absent; beak lateral, erect, 0.2--0.5 mm.

Flowering summer--fall. Rice fields, ephemeral pools, roadside ditches, and streams; 0--100 m; introduced; La.; c, s Mexico; West Indies; Central America; tropical South America.