Perennial, 11-47 cm, forming tight tufts. Rhizome short. Stem 0.5-1.3 mm diam., terete, deeply grooved, smooth, occasionally scabrous. Leaves from c. 2/3 to equalling stem, rigid or often flexuous above, mostly less wide than stem; sheaths 20-75 mm (old sheaths often of equal length), from dark brown to almost black, glossy, sometimes disintegrating into fibres, mouth margin deeply oblique; ligule c. 0.2 mm, slightly arched; blades 1-1.5 mm wide, channelled or inrolled, not keeled, margins scabrous, apex long-attenuate, trigonous, scabrous. Inflorescence 10-46 x 2-4 mm, cylindrical or clavate, composed by from 9 to more than 20 glumes, partial inflorescences, each with one basal pistillate flower (lower occasionally with 2-3 pistillate flowers) and 0-5 staminate flowers on rachilla above; glume-like bracts 3.5-6 mm, longer than partial inflorescence, wide-clasping, from dark to yellowish brown, margins and apex rounded, often widely scarious; utricle 2.7-4.3 mm, glume-like, sheathing, 2-keeled, cymbiform, margins of basal part fused for 0.3-1.1 mm, light brown, apex rounded, narrowly scarious; style 1.5-2 mm, stigmas 3; staminate glumes 2.6-4.6 mm, rather narrow, folded, apex rounded; stamens 2-3. Nut 2.7-3.5 x 1-1.5 mm, obovoid, obtusely trigonous, plano-convex, yellowish or grey-brown, glossy, finely reticulate.