Herbs, perennial, cespitose, rhizomatous. Culms roundly tri-gonous, 80-120 cm × 3-6 mm, glabrous. Leaves 5-12, V-shaped, 30-75 cm × 8-14 mm, septate, leathery, margins harshly scabrid. Inflorescences: spikes 1-4 per ray, loosely ovoid to broadly ellipsoid, 12-20 × 8-12 mm; rays 6-9, 3-10(-12) cm; 2d order rays 1-4, 1-2 cm; rachis 4-12 mm; bracts 5-10, horizontal to ascending at 30°, 15-40 cm × 4-8(-11) mm; rachilla deciduous, wings persistent, hyaline, fragile, 0.3 mm wide, covering less than 1/2 of achene. Spikelets 40-80, narrowly ellipsoid to ellipsoid, roughly quadrangular to weakly flattened, 5-8 × 1.2-1.5 mm; distal spikelet spreading or ascending; floral scales (1-)2(-3), ascending, brick red, medially greenish, laterally 3-4-ribbed, medially 1-3-ribbed, green, ovate, 2.2-3.5 × 1.5-1.8 mm, apex subacute. Flowers: anthers (0.7-)1-1.5 mm, filaments 4-4.7 mm; styles 0.5-0.9 mm; stigmas 2-3 mm. Achenes brown, ellipsoid to oblong-fusiform, 1.7-1.8 × 0.7 mm, base cuneate, apex subacute and apiculate, surfaces finely puncticulate to glabrous.

Fruiting spring-fall. Disturbed, damp thickets, open woods; 0-200 m; introduced; Calif.; s Africa.

Cyperus owanii is easily distinguished from other sedges in California by the large size, reddish spikelets, and secondary rays. It was first collected in California in 1938.