Herbs, perennial, to 100 cm; rhizomes absent; stolons present; corms present. Leaves emersed; petiole 5-ridged, ascending to erect, 24.5--60 cm; blade sagittate, 11.5--26.5 ´ 0.8--15 cm, basal lobes longer than remainder of blade. Inflorescences racemes, rarely panicles, of 5--17 whorls, emersed, 20--37 ´ 5--27 cm; peduncles 25--96 cm; bracts connate more than or equal to ¼ total length, lanceolate, 6.5--15 mm, delicate, not papillose; fruiting pedicels spreading, cylindric, 1.5--4.4 cm. Flowers to 3 cm diam.; sepals recurved to spreading, not enclosing flower; filaments cylindric, shorter than anthers, glabrous; pistillate flowers pedicellate, without ring of sterile stamens. Fruiting heads 0.9--1.5 cm diam; achenes oblanceoloid, abaxially keeled, 1.2--2.5 ´ 0.8--1.6 mm, beaked; faces tuberculate, wings absent, glands 0--1; beak lateral, erect, 0.1--0.6 mm. Flowering summer--fall. Wet ditches, ephermeral pools, and margins of streams and lakes; 0--300 m; Ariz., Calif., Kans., Nebr., Okla., Tex.; Mexico; Central America (Nicaragua).