Herbs, annual or perennial, cespitose; stolons slender, to 5 cm × 1.5 mm. Culms trigonous, 25-90 cm × 2 mm, hispidulous or glabrous on angles distally. Leaves flat, 10-35 cm × 3-10 mm. Inflorescences: spikes 1-4(-6), loosely oblong-ovoid, 2-3 × 1-2 cm; rays 3-10, 1-16 cm; 2d order rays to 3 cm; rachis hispidulous, prickles slender, 0.1-0.2 mm; bracts 3-5, ± ascending, flat, 5-35 cm × 0.5-5(-7) mm; rachilla persistent, wingless. Spikelets 15-40, linear-lanceoloid, compressed, 6-12 × 1.5-2 mm; floral scales deciduous, 8-16, light brown with clear border, laterally 2-3-ribbed, ovate, 1.8-2 × 1.2-1.6 mm; apex entire, emarginate, or mucronulate, mucro at most 0.3 mm. Flowers: anthers 0.4 mm; styles 0.6 mm; stigmas 1 mm. Achenes brown, sessile, broadly ellipsoid, 1-1.2 × 0.5 mm, apex obtuse, apiculate, surfaces puncticulate.

Fruiting summer. Rice fields, wetlands, emergent muddy shores; 0-50 m; introduced; Fla., La., Miss., S.C.; Asia.

Cyperus pilosus was naturalized in the flora from eastern Asia, apparently early in the twentieth century.

The combination of hispidulous rachis and loosely oblong-ovoid spikes is sufficient to distinguish Cyperus pilosus from any others with deciduous floral scales.