Cyperus autumnalis Vahl; C. haspan subsp. juncoides (Lamarck) Kükenthal; C. haspan var. americanus Boeckeler; C. juncoides Lamarck

Herbs, perennial, cespitose, shortly rhizomatous. Culms trigonous, (2–)25–60(–100) cm × 1–4 mm, soft (flattened in drying), glabrous. Leaves usually reduced to sheaths, occasionally with blades, flat to V-shaped, (3–)10–30 cm × (1–)2.5–5 mm. Inflorescences: heads loosely digitate; rays (5–)10–12(–15), 1–15(–20) cm; 2d order rays usually present, (1–)6–12(–25) mm; 3d order rays sometimes present, 1–6 mm; bracts 2(–3), horizontal to ascending at 30–60°, longer (3–)6–18 cm × 2–4 mm, shorter (0.5–)2.5–6.5 cm × 1–2(–3) mm. Spikelets 1–15, linear-lanceoloid, ± compressed-quadrangular, 3–18 × 1–1.6 mm; floral scales 10–20(–40), laterally reddish to greenish brown, dull, often clear-edged, medially greenish, laterally 1-ribbed, medially 1-ribbed, oblong to obovate, 1–1.5(–1.9) × 0.8–1 mm, apex mucronate, glabrous except for cluster of crystalline prickles at apex. Flowers: stamens 3; anthers 0.3–0.5 mm; styles 0.4–0.9 mm; stigmas 0.5–0.8(–1.3) mm. Achenes white or reddish brown, stipitate, globose to obovoid or ellipsoid, 0.5–0.6(–0.7) × 0.3–0.4(–0.5) mm, base nearly cuneate, stipe 0.1 × 0.1–0.2 mm, apex obtuse to acute, apiculate or entire, surfaces granular to papillose.

Fruiting summer. Swales between dunes, marshes, pond shores; 0–200 m; Ala., Fla., Ga., La., Miss., N.C., S.C., Tex., Va.; Mexico; Central America; South America; Asia; Africa; Australia.