Rhizomes to 20 cm × 10 mm. Culms 1-2 m × 5-10 mm. Leaves: blades flat to broadly V-shaped, 1-2 m × 7-10 mm, margins and midvein abaxially harshly scabrous with teeth visible to unaided eye. Inflorescences terminal (or lateral and terminal), pedunculate, peduncle mostly covered by subtending leaf sheath, 30-50 cm; 1st, 2d, 3d, and rarely 4th order branches, branches slightly flexuous. Spikelets in groups of (3-)4-6, ellipsoid to lanceolate, 3 mm; floral scales 5-6, the proximal chestnut brown, ovate to oblong-lanceolate, 2.5-3 × 2 mm, midvein conspicuous, lateral veins weak; stamens 2; anthers 2 mm, connective apices 0.1 mm; styles 1-1.5 mm; stigmas 1-1.5 mm. Achenes purplish brown, ovoid, 1.5-2 × 1 mm, base vaguely 3-lobed, truncate, not flared or discoid, apex acute, persistent style base forming beak 0.2 mm, smooth or irregularly rugulose, glossy. 2n = 36. Fruiting and flowering late spring-summer. Alkaline marshes, swamps, springs; 0-2000 m; Ariz., Calif., Nev., Tex., Utah; Mexico (Coahuila). Cladium californicum is chiefly differentiated from C. jamaicense by distribution. A detailed investigation of the morphologic differences between the two species would be instructive.