Description from Flora of China
Annuals or short-lived perennials. Rhizomes absent or very short. Culms tufted, 15-50 cm tall, thin, flatly 4-angled, striate, bearing 1 or 2 bladeless sheaths at base. Basal leaf sheaths 2.5-6.5 cm, cylindric, covered with fibers from old sheaths, mouth obliquely truncate, apex acute. Leaves shorter than to subequaling culm; sheath adaxially membranous and rust-colored, mouth obliquely split; ligule absent; leaf blade 1.2-2.2 mm wide, flat, margin finely toothed, apex acute. Involucral bracts 4-6, setaceous, much shorter than inflorescence, base dilated, margin finely serrulate. Inflorescence a simple or subcompound anthela, 1.5-6 × 2-6 cm; rays 4-8, 0.6-4 cm, scabrid. Spikelets solitary, obovoid to oblong-obovoid, 2.5-7.5 × 1.5-2.5(-3) mm, densely many flowered, apex obtuse to subacute. Glumes reddish brown or straw-yellow, broadly ovate or oblong-ovate, ca. 2 mm or slightly longer, membranous, 3-veined forming a slight abaxial keel, veins green, margin hyaline, apex extremely obtuse. Stamens 2; anthers oblong, ca. 0.8 mm, ca. 1/2 as long as filaments, apex obtuse. Style not ciliate, basally slightly inflated; stigmas 2 or 3, subequaling to slightly longer than style. Nutlet brown, broadly obovoid, ca. 1 mm, 3-sided or biconvex, with sparsely verruculose and with transversely oblong reticulation. Fl. and fr. Jun-Sep.
Paddy fields, streamsides, wet places in valleys, ponds; 100-2100 m. Anhui, Chongqing, Fujian, Guangdong, Guangxi, Guizhou, S Henan, Hubei, Hunan, Jiangsu, Jiangxi, Shandong, Sichuan, Zhejiang [Japan, Korea].