Herbs, perennial, cespitose, rhizomatous. Culms trigonous, 30-150 cm × 1-5(-8) mm. Leaves bladeless. Inflorescences: heads digitate, 15-30(-36) mm diam.; rays (14-)20-22, (2-)5-12(-20) cm; 2d order rays 0.3-3(-4) cm; 3d order rays sometimes present, 0.3-2.5 cm; bracts (4-)18-22, ± horizontal, flat, 15-27 cm × (1.5-)8-12 mm. Spikelets 8-20, ovoid to linear-lanceoloid, compressed, 5-25 × 1.5-2 mm; floral scales 8-28, laterally whitish or light brown, ± hyaline, medially light brown, laterally ribless, medially 3-ribbed, 2-keeled in proximal 30-60%, deltate-ovate, 1.6-2.4 × (1-)1.2-1.5(-1.7) mm, apex acute. Flowers: stamens 3; anthers 0.7-1 mm; styles 0.5-1 mm; stigmas 0.6-1 mm. Achenes brown, sessile or stipitate, broadly ellipsoid, 0.6-0.8 × 0.4-0.6 mm, stipe if present to 0.1 mm, apex obtuse, apiculate, surfaces puncticulate. Fruiting early summer-fall. Damp, disturbed soils, ditches, stream banks; 0-100(-800) m; introduced; Calif., Fla., La., Tex.; e Africa. Cyperus involucratus has been collected in New York (R. S. Mitchell and G. C. Tucker 1997). Cyperus involucratus is widely cultivated as a water plant in greenhouses and outdoors in warm-temperate or tropical climates. It has long been misidentified in the flora as C. alternifolius Linnaeus, an endemic of Madagascar (G. C. Tucker 1983).