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Herbs, annual, cespitose. Culms trigonous, (5–)20–60 cm × (0.2–)0.6–2.4 mm, glabrous. Leaves (1–)3–4, V-shaped, 15–40 cm × 3–6 mm. Inflorescences: spikes 2–5(–8), oblong to ovoid, 2–10 cm × 3–12 mm; rays 4–8, to 11 cm; bracts (4–)5(–7), ascending at 45°, V-shaped, (1.5–)8–30(–50) cm × 1–6 mm; rachilla persistent, wingless (successive floral scales 1.1–1.5 mm apart). Spikelets 10–30, spreading, compressed, linear, 4–20 × 1.5–2.1 mm; floral scales deciduous, (2–)6–26, laterally brown to golden brown, edges clear, medially green, 5-ribbed, outermost ribs more noticeable than others, obovate to nearly orbiculate, 1.3–1.8 × 1.2–1.8 mm, margins emarginate, apex mucronulate, mucro 0.2–0.25 mm. Flowers: stamens 2(–3); anthers (0.2–)0.3–0.4 mm, tips of connectives reddish, less than 0.1 mm; styles less than 0.1 mm; stigmas 0.2–0.4(–0.5) mm. Achenes brown, slightly stipitate, obovoid, 1.2–1.4(–1.5) × 0.5–0.7 mm, apex apiculate, surfaces puncticulate.
Much like no. 9 [Cyperus iria L.]; spikes 2–4 cm; rachilla narrowly winged; scales truncate, with an evident green mucro to 0.4 mm. Native to e. Asia, intro. on L.I. and in e. Pa. (C. amuricus, at least as applied to our plants)
