Description from Flora of China
Scirpus spiralis Rottbøll, Descr. Icon. Rar. Pl. 45. 1773.
Perennials. Stolons slender. Culms erect, pale green, tufted, 50-60 cm tall, 3-4 mm thick, firm, 3-angled, without transverse septa and nodes. Leaf sheaths 3 or 4, 3-21 cm, smooth, slightly shiny; basalmost sheath purplish red to dark brown, ± short; cauline sheaths pale red, elongate, mouth obliquely truncate and parted, apex shortly acuminate with a setaceous appendage. Spikelet pale yellow, cylindric, 1.5-3 cm × 5-6 mm, many flowered, apex acute to obtuse. Basalmost glume empty, broadly triangular, amplexicaul for whole spikelet base; fertile glumes densely imbricate, subquadrate, ca. 3 × 3 mm, pale and brownish red puncticulate striate, medially leathery and with a midvein, margin hyaline and minutely brown puncticulate, apex truncate to subtruncate. Perianth bristles 6, reddish purple, as long as or shorter than nutlet, laxly retrorsely spinulose. Stigmas 3. Nutlet pale yellow turning dark brown when mature, obovoid to broadly obovoid, 1.2-1.5 × ca. 1 mm, compressed biconvex, obscurely cancellate with 17-20 rows of transversely oblong epidermal cells, margin narrow, apex not constricted but with an obscure annular thickening; persistent style base conic, basally gradually narrowed, base ca. 1/2 as wide as nutlet. Fl. and fr. Nov-Jan.
Wet places near seashores; near sea level. Guangdong, Hainan [Bangladesh, Cambodia, India, Indonesia, Malaysia, Myanmar, Papua New Guinea, Philippines, Sri Lanka, Thailand, Vietnam; tropical Africa and Australia, Madagascar, Pacific islands].