Perennial. Leaves rigid, linear, 10-50 cm by 1½-3½ mm, acute, often falcate, twisted, widened at the base, striate when dry, with a stout nerve in either margin, which is scabrous but for the basal part. Sheaths narrow, 3-7 cm, slightly crested. Peduncle 10-60 cm by 2-2½ mm, distinctly compressed, twisted, with a stout, scabrous rib in either margin. Head oblong-ovoid to cylindrical, 5-25 by 4-7 mm. Basal bracts elliptic, 2-4 by 2-3 mm, with ca 1 descending nerves; median bracts elliptic to orbicular, 5-6 by 4-6 mm, sometimes with a prominulous keel, central part subspinulose at the top, papillate in a triangular field in the upper half, entire or emarginate at the top, with ca 15 descending nerves. Lateral sepals 4-5 by 1-1½ mm, obtuse, top sometimes scarious, crest lacerate-fimbriate in the upper half, sometimes exceeding the top; median sepal cap-shaped, 3-3½ mm long, with 1 or 3 nerves. Petals 5-6 mm long, limb obtriangular to obovate, ca 3 mm by 3-4 mm, apical margin lacerate, claw 2½-3 by ca ½ mm. Stamens 2-2½ mm, filament ca 1 mm; anthers 1-1½ mm, deeply incised at the top, cells with 2 acute tips, base mucronulate or with 2 acute tips. Staminodes bifid, penicillate, ca 1 mm long. Ovary obovoid, 3-sided, ca 2 by 1 mm. Styles 3-fid, 3-5 mm, arms ca 1 mm, infundibuliform at the top, with lacerate margins. Fruit 3-3½ by 2½-3 mm.
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Herbs perennial. Leaf sheath narrow, 3.5--7.5 cm; leaf blade linear, (5--)10--25(--40) cm × 1--3.5 mm, rigid, thick, striate when dry, margin thickened and with a stout vein, apex acute. Peduncle erect, 10--40(--60) cm × 1.2--2.5 mm, distinctly compressed, usually twisted leftward, margin with a stout, scabrous rib. Spikes oblong-ovoid to cylindric, 8--20 × 5--8 mm; bracts brownish, suborbicular to broadly obovate, 5--5.5 × 4--5 mm, sometimes with a prominent keel, abaxially subspinulose at center, apical part with a triangular, papillose patch, apex obtuse. Lateral sepals boat-shaped, 3.8--4.5 × 1--1.5 mm, keel lacerate-fimbriate in apical 1/2; median sepal hooded, 3--3.5 mm, veins 1 or 3. Petals yellow; limb obovate to obtriangular, 5--6 mm, apical margin lacerate; claw narrow. Stamens 3; filaments ca. 1 mm; anthers 1--1.5 mm, apex deeply incised; locules mucronulate at base, apex with 2 acute points. Staminodes 2-cleft, ca. 1.5 mm. Ovary obovoid. Style 3--5 mm; stigma funnelform, margin lacerate. Capsule ovoid, 3--3.5 mm. Seeds ovoid to ellipsoid, ca. 0.4 mm. Fl. Aug--Sep, fr. Sep--Oct.
Open, wet places on sandy soil, often among grasses and Sphagnum, from sea level to 1600 m, fl. April-Jan.
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