Herbs, perennial, rhizomatous, stout. Culms roundly trigonous, 200-350 cm × 15-50 mm, glabrous. Leaves bladeless. Inflorescences: spikes loosely cylindric, 15-40 × 8-16 mm; rays 5-8, ascending to erect, stiff,20-30 cm; 2d order rays 5-15 cm; bracts 10-12, ascending at 30-60°, flat, (8-) 20-45 cm × 4-12 mm; 2d order bracts (5-)15-25 cm × 1.5-5 mm; rachilla persistent, separating laterally, remaining firmly attached basally, wings 0.3-0.4 mm wide. Spikelets (15-)50-80, slightly compressed, linear, ± quadrangular, 5-12 × 0.6-1.4 mm; floral scales 8-20, appressed, reddish beside 5-ribbed green medial part, white to hyaline near margins, ovate, 1.8-2.2 × 1.2-1.5 mm, apex acute to obtuse. Flowers: anthers 0.7-1 mm (connective prolonged beyond anther as red subulate appendage 0.2-0.5 mm, its apex sometimes setose); styles 0.2-0.5 mm; stigmas (0.8-)1.2-1.8 mm. Achenes pale brown, sessile, oblong, 0.9-1 × 0.4-0.5 mm, apex scarcely apiculate, surfaces puncticulate.

Fruiting summer. Stream banks, marshes; 0-10 m; introduced; La., Tex.; Mexico; West Indies; Central America; South America.

Cyperus giganteus was erroneously reported from Florida, a misidentification of C. papyrus (R. R. Haynes and A. Lasseigne 1969).