Herbs, perennial, rhizomatous. Culms trigonous, (10-)30-80(-140) cm × (0.4-)1-3(-5) mm, glabrous. Leaves V-shaped or flanged V-shaped, (5-)15-70(-90) cm × (2-)4-10(-13) mm, glabrous. Inflorescences: spikes 1(-5), rather densely ovoid or oblong-cylindric, (10-)25-45(-62) × 7-22 mm, 11-21 spikelets per 5 mm of rachis; rays (3-)5-10(-17), (1-)5-12(-24) cm; bracts (2-)4-8, ascending at 30-45°, V- or inversely W-shaped, (2-)8-40(-65) cm × (1-)2-8 mm; rachilla deciduous, wings 0.4-0.5 mm wide. Spikelets (10-)50-150, oblong to linear, quadrangular, (3-)4-8(-18) × (0.8-)1-1.2(-1.6) mm; distal spikelet spreading or ascending; floral scales (1-) 3-8, pale greenish white to golden brown, deep brown, or reddish brown, medially usually green, weakly to strongly 3(-4)-ribbed laterally, 1-3-ribbed medially, ovate to elliptic, (2-)2.6-3.2(-4) × 1.2-2 mm, apex obtuse. Flowers: anthers (0.4-)0.6-1 mm; styles 0.4-1.6 mm; stigmas 1-1.5 mm. Achenes brown or reddish brown, sessile or nearly so, ellipsoid, 1.4-1.8(-2) × 0.6-0.8(-1) mm, apex acute to obtuse, slightly apiculate, surfaces puncticulate. Fruiting summer-fall. Arroyos; 500-1200 m; Ariz., Tex.; Mexico; West Indies; South America. An erroneous report of Cyperus hermaphroditus from Alabama was based on misidentification of C. thyrsiflorus.