Description from Flora of China
Cyperus unioloides R. Brown, Prodr. 216. 1810; Pycreus chekiangensis Tang & F. T. Wang.
Perennials. Rhizomes short. Culms tufted, 40-90 cm tall, slender, stiff, 3-angled, smooth, with a few leaves basally. Leaves shorter than culm; sheath reddish brown, to 8 cm; leaf blade 3-4 mm wide, folded or flat, somewhat rigid. Involucral bracts 2-4, leaflike, basal 1 or 2 longer than inflorescence. Inflorescence a simple anthela; rays 2-6, mostly to 6 cm, sometimes short, each with 3-12 spikelets arranged into a spike. Spikelets narrowly oblong-ovoid, narrowly ovoid, or oblong-ovoid, 0.6-1.8 cm × 3-5 mm, compressed, spreading to downward reflexed at basal part at maturity, (6-)10-22-flowered; rachilla flexuose, wingless. Glumes straw-colored, yellowish brown, or sometimes slightly reddish brown on both surfaces, slightly densely to slightly laxly imbricate, ovate, 4-5 mm, subleathery, veins 3 and green, apex acute. Stamens 3; anthers linear; connective prominent beyond anthers. Style long; stigmas 2, slightly shorter than style. Nutlet yellowish when young but black when mature, broadly obovoid to globose-obovoid, 1/4-1/3 as long as subtending glume, compressed biconvex, densely prominently puncticulate. Fl. and fr. Jun-Oct.
Pycreus chekiangensis appears to be based on immature plants of P. unioloides. Although the glumes are lighter, this variation can be found in P. unioloides in various parts of its pantropical range.
Wet places, river margins in valleys; 200-2200 m. Guangdong, Taiwan, Yunnan, Zhejiang [Bhutan, Cambodia, India, Indonesia, Japan, Myanmar, Nepal, Papua New Guinea, Philippines, Thailand, Vietnam; Africa, E Australia, Central, North, and South America, Madagascar].