Perennial, with short rhizome; long slender stolons sometimes present. Stems erect, tufted, slender, rigid, acutely 4-angled, with usually prominently ribbed angles and finely longitudinally striate or rather prominently ribbed sides, smooth, (15-)30-70 cm by 1-1½ mm. Sheaths herbaceous, closely appressed, purplish below, the upper one slightly thickened and brownish at the mouth, truncate or somewhat oblique, shortly mucronate just below the apex. Spikelet ovoid to oblong-ellipsoid, broader than the stem, often somewhat inclined, terete, acute, densely many-flowered, ferrugineous to brown, 10-20 by 3-5 mm. Glumes rather firm, rather densely imbricate, closely appressed when young, somewhat spreading with age, elliptic to oblong-elliptic or lanceolate, obtuse, not or only faintly keeled, 1-nerved, ferrugineous with paler keel and narrow scarious margins, 3-4 by c. 2 mm. Bristles 6, coarse, flat, about as long as or slightly exceeding the nut including the style-base, very densely retrorsely scabrous or subplumose, rufous. Style 3-fid. Stamens 2-3; anthers linear, minutely apiculate, 1-1½ mm. Nut obtusely trigonous, compressed, obovoid, not constricted below the apex, shining, yellowish or olivaceous to brown, obsoletely reticulate by the small, vertically oblong epidermal cells, 1¼-1½ by 9/10-1.2 mm. Style-base large, deltoid to submitri-form, compressed above, somewhat pyramidal below, spongious, fuscous, c. ½-¾ as long and ½-4/5 as wide as the nut.
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Perennials. Stolons short or absent. Culms tufted, 25-90(-100) cm tall, ca. 1 mm thick, sharply 4-angled, glabrous. Leaf sheaths 2 or 3, tubular, 7-10 cm, basally purplish red, apically grayish green, mouth truncate, apex shortly triangular and mucronate. Spikelet brownish green, oblong-ovoid, ± narrowly ovoid, or oblong, 7-20 cm × 3-5 mm, slightly oblique, many flowered, apex obtuse to acute. Basal 3 glumes empty; basalmost glume amplexicaul for whole spikelet base; fertile glumes green at middle and pale rust-colored on sides, tightly imbricate, oblong and boat-shaped, 3-4 × 1-1.5 mm, papery, margin narrowly hyaline, apex obtuse. Perianth bristles 6, reddish to brownish, as long as nutlet (including style base), laxly to densely retrorsely spinulose. Stigmas 3. Nutlet pale brown when mature, with a short thick stipe, obovoid to broadly obovoid, ca. 1.2 × 1.5 mm, compressed 3-sided; persistent style base laterally compressed, deltoid, 1/2-2/3 as long and ca. 3/4 as wide as nutlet, surface sometimes mammillate, apex acuminate. Fl. and fr. Sep-Nov.
Open swampy places, at medium and high altitudes (in Java between 1000 and 2200 m, in the Philippines between 650 and 1800 m, in Sumatra Eastcoast Res. descending to 450 m), rarely ascending to 2700 m (W. and NE. New Guinea).
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