Herbs, annual, densely cespitose, with fibrous roots. Culms roundly trigonous, 3-25(-30) cm × 0.3-1.4 mm, glabrous. Leaves 1-3, V-shaped, 1-8 cm × 1-2 mm. Inflorescences: spike 1, loosely ovoid, compressed, 7-14 × 9-14 mm; rays 1-4, to 2(-3) cm; bracts 2-3, horizontal to ascending at 30(-45)°, V-shaped to flat, 1-12 cm × 0.5-1.5 mm. Spikelets 3-5(-8), flattened, oblong to oblong-lanceoloid, 8-18 × 2-2.6(-3) mm; floral scales (6-)10-26(-32), closely imbricate, laterally light to dark brown, medially light brown, laterally ribless, medially 2-3-ribbed, 2-keeled, oblong to ovate, 1.9-2.7 × 1.8-2.3 mm, apex obtuse. Flowers: stamens 2-3; anthers 0.4-0.5 mm, connective not prolonged; styles 0.6-1 mm; stigmas 1-1.5 mm. Achenes black, network of ridges forming isodiametric or square cells, sessile, obovoid to ovoid, 1-1.3(-1.5) × (0.6-)0.8 mm, apex apiculate, surfaces minutely punctate. Fruiting summer. Emergent shorelines, ditches, puddles, often in disturbed places; 0-1500 m; Ont., Que.; Ala., Ariz., Ark., Calif., Colo., Conn., Del., D.C., Ga., Ill., Ind., Iowa, Kans., Ky., La., Maine, Md., Mass., Mich., Minn., Miss., Mo., Nebr., Nev., N.H., N.J., N.Mex., N.Y., N.C., N.Dak., Ohio, Okla., Oreg., Pa., R.I., S.C., S.Dak., Tenn., Tex., Utah, Vt., Va., Wash., W.Va., Wis.; Mexico; Central America; South America.