Description from Flora of China
Cyperus polystachyos Rottbøll, Descr. Pl. Rar. 21. 1772; Pycreus polystachyos var. brevispiculatus How ex Y. F. Deng.
Annuals or short-lived perennials. Roots fibrous. Rhizomes short. Culms densely tufted, 8-60 cm tall, compressed 3-angled, stiff, smooth. Leaves shorter than culm; sheath brown at basal part, long; leaf blade 2-4 mm wide, flat, sometimes folded, slightly rigid. Involucral bracts 4-6, leaflike, longer than inflorescence. Inflorescence a simple or almost capitate anthela; rays 5-8, mostly to 3.5 cm but sometimes short, each with many spikelets. Spikelets linear to linear-oblong, (0.5-)0.7-1.8 cm × 1.5-2 mm, congested into a globose spike, 6-30-flowered or more; rachilla flexuose, narrowly winged. Glumes on both surfaces straw-colored, reddish brown, dark grayish brown, or blackish dark grayish brown, densely imbricate, ovate-oblong, ca. 2 mm, membranous, 3-veined, keel abaxially green, apex sometimes mucronate. Stamens (1 or)2; anthers linear; connective prominent beyond anthers. Style long; stigmas 2, slender. Nutlet suboblong to ovoid-oblong, ca. 1/2 as long as subtending glume, biconvex, puncticulate, apex mucronate. Fl. and fr. May-Oct.
Plants with anthela rays short or nearly absent occur sporadically throughout the range of this pantropical and warm-temperate species. Such plants have been collected in S China (Guangdong) and given the name Pycreus polystachyos var. brevispiculatus. When the species is revised on a worldwide basis, it may be appropriate to provide a formal designation for these plants with a capitulum-like inflorescence.
Wet places, sandy areas at seashores, water margins, shady areas in wet sand, paddy field margins; near sea level to 300 m. Fujian, Guangdong, E Guangxi, Hainan, Jiangsu, S Liaoning, Taiwan, Xisha Qundao, Zhejiang [Cambodia, India, Indonesia, Japan, Korea, Laos, Malaysia, Myanmar, Pakistan, Philippines, Russia (Far East), Sri Lanka, Thailand, Vietnam; Africa, SW Asia, Australia, Central, North, and South America, S Europe, Indian Ocean islands, Madagascar, Pacific islands].