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. Fruiting summer. Disturbed soils; 0-100 m; introduced; Conn., Ky., Mass., N.J., N.Y., Ohio, Pa.; e Asia. The name Cyperus amuricus Maximowicz has been misapplied to C. microiria by some American authors (e.g., M. V. McGivney 1938).
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)
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
