Herbs, perennial, cespitose, rhizomatous. Culms trigonous to terete, (25-)40-60(-90) cm, glabrous. Leaves flat or V-shaped, (10-)25-50 cm × 5-8(-12) mm. Inflorescences: heads globose, (10-)20-40 mm diam.; rays (0-)3-10, 2.5-5(-12) cm; 2d order rays usually absent (when present, 0.5-1.5 cm); bracts 4-8, horizontal to ascending at 15-30°, flat (or V-shaped), 3-30(-50) cm × 1.5-8(-12) mm. Spikelets (20-)30-50(-70), oblong, compressed, 5-20 × 2.2-3 mm; floral scales (12-)20-30(-50), off-white to golden brown, basally 2-keeled, laterally ribless, ovate-deltate, 2-2.3 × 1-1.4 mm (declined 30-40º from rachilla). Flowers: stamen 1; anthers 1-1.2 mm; styles 1-1.2 mm; stigmas 0.5 mm. Achenes black or dark brown, stipitate, broadly ellipsoid, 1.2-1.4 × 0.5-0.6 mm, stipe to 0.1 mm, apex apiculate, beak 0.2-0.3 mm, surfaces puncticulate.

Fruiting summer. Damp grasslands, roadsides ditches; 0-200 m; B.C.; Ala., Calif., La., Miss., N.J., Oreg., Pa., S.C., Tex., Wash.; South America; naturalized, Europe.

The distributions of Cyperus eragrostis in British Columbia, Alabama, Pennsylvania, South Carolina, and Texas represent introduced populations.