Description from Flora of China
Cyperus amuricus Maximowicz var. japonicus Kükenthal (1936), not Miquel (1866).
Annuals. Roots fibrous. Culms tufted, 20-60 cm tall, slightly slender, acutely triquetrous, smooth, base several leaved. Leaves shorter than or equaling culm; sheath purplish brown; leaf blade ca. 2.5 mm wide, flat. Involucral bracts 3 or 4(or more), leaflike, longer than inflorescence. Inflorescence a compound or decompound anthela; rays 5-9, mostly to 13 cm, unequal in length. Spikes ovoid, broadly ovoid, or subconic, 2-4 × 1-3 cm, with many spikelets. Spikelets slightly laxly arranged, linear to very narrowly linear-ovoid, 0.6-1.5 cm × ca. 1.5 mm, obliquely spreading to spreading, 8-24-flowered; rachilla wings white, narrow, straight, hyaline; successive glumes on rachilla 1-1.5 mm apart. Glumes straw-colored to pale, lax, broadly obovate, ca. 1.5 mm, membranous, 3-5-veined and green, keel abaxially extended beyond apex into a mucro, apex rounded. Stamens 2(or 3); anthers oblong, 0.2-0.4 mm. Style very short; stigmas 3, ± short. Nutlet dark brown, oblong-obovoid, 1.2-1.5 mm, nearly as long as subtending glume, 3-sided, densely prominently puncticulate. Fl. and fr. Aug-Oct.
Cyperus microiria is naturalized in S Australia and North America.
Forests, under shrubs, grasslands on mountain slopes, wet places by river margins, ditch margins, water margins, seashores, along trails, paddy fields; near sea level to 3800 m. Anhui, Chongqing, Fujian, Gansu, Guangdong, Guangxi, Guizhou, Hebei, Henan, Hubei, Hunan, Jiangsu, Jiangxi, S Jilin, Liaoning, NE Nei Mongol, Shaanxi, Shandong, Shanxi, Sichuan, E Yunnan, Zhejiang [India, Japan, Korea, Thailand, Vietnam].