Annuals. Rhizomes short. Culms tufted, 7-40 cm tall, 3-angled, striate-sulcate, pubescent, clothed at base with 1 or 2 bladeless pubescent leaf sheaths. Cauline leaves with sheath 1-3.5 cm; ligule rust-colored to reddish, 1-2 mm, membranous, mouth truncate; leaf blade linear, 5-15 × 3-7 mm, flat, soft, 3-costate, surfaces and margin ± pubescent, apex acuminate. Involucral bracts leaflike, surpassing inflorescence; bractlets setaceous, sheathless. Inflorescences with 1-3 clusters of spikelets, interrupted, glomerulate, 1-3 cm wide, bearing 3-15 spikelets; peduncles single, mostly enclosed in bractlet sheaths. Spikelets ovoid to oblong, 5-8 × 2.5-3 mm, many flowered, covered with woolly hairs. Glumes basally yellowish brown, apically grayish black, obovate, 1.2-2 mm, thinly membranous, abaxially pilose, apex obtuse, emarginate, and with a 3-veined costa excurrent into a recurved 1-1.5 mm awn. Perianth bristles 6; 3 outer bristles needlelike, occasionally much reduced, retrorsely scabrous; 3 inner bristles brownish, with subquadrate blades abruptly narrowed at base to a distinct ca. 0.3 mm stalk, apex mucronulate. Stamens 3; anthers oblong, 0.2-0.3 mm. Ovary white, oblong, 3-sided; style brownish, 3-4 × as long as ovary; stigmas 3, 1/3-1/2 as long as style. Nutlet brownish, shortly stipitate, obovoid, ca. 1 mm, 3-sided. Fl. and fr. Jul-Dec. 2n = 38.
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Annual. Stems slender, obtusangular, striate-sul-cate, pubescent at the top or sometimes throughout, (5-)10-40 cm by 1-2 mm, not incrassate at the base. Leaves rather weak, more or less pubescent or at least ciliate on the margins, with 3-5 more prominent nerves, light green, 3-8 mm wide; sheaths pubescent. Inflorescence sometimes a single terminal cluster, but usually also with 1-2 clusters on short pubescent peduncles in the upper axils. Glumes obovate to oblong-obovate, short-hairy almost throughout the back, pilose in the centre, 1½-1¾ by c. 1¼ mm (the c. 1 mm long awn excluded). Perianth biseriate: bristles scaberulous or almost smooth, sometimes as long as the nut, usually much shorter; scales distinctly clawed, subquadrate, cordate or hastate at the base, with 3 minute teeth at the distinctly thickened top (central tooth largest), glabrous or minutely hairy at the apex. Anthers oblong, c. ¼ mm long. Nut slightly smaller than in F. umbellata, ¾-1 by 0.5-0.6 mm. Otherwise as F. umbellata.
Perennial herb, up to 400 mm tall. Stamens 3. Spikelets 2.0-3.2 mm wide. Nutlets (0.7-)0.8-l,l(-l,3) mm long. Glumes awned. Awns with long bristles. Glumes green.
In open wet lands: in swampy grassland, on riverbanks, and especially in wet rice-fields, at low altitudes (in Java up to 800 m, in Atjeh collected at 1180 m), usually scattered but sometimes abundant.