Plants loosely cespitose; rhizomes short, slender. Culms to 30(-60) cm. Leaves: blades 2-4 mm wide. Inflorescences 2-6(-8) cm; proximal internode 10-40 mm; peduncle of proximal spikes exserted to 4 cm; proximal bracts with blade 5-22 mm, sheath cylindric, 5-28 mm, mouth usually tinged with dark purple, 0.9-1.4 mm wide Spikes 2-5; lateral spikes usually pistillate, inclined or pendent, 8-19 × 4-7 mm; terminal spike staminate or gynecandrous, erect or inclined, 6-15 × 2-5 mm. Pistillate scales black with pale midvein, ovate or oblong-ovate, 3-4.8 × 0.9-1.6 mm, margins narrow and scarious, apex acute to obtuse, papillose at least on midvein. Staminate scales black with pale midvein, oblong-obovate, 3-5 × 1.2-1.8 mm, margins scarious, apex acute or obtuse. Anthers 1.9-2.6 mm. Perigynia ascending, pale brown proximally, black distally, indistinctly veined, ovate, 3-4.8(-5.5) × 0.9-1.6 mm, papillose at least on margins; beak distinct, 0.3-0.5 mm. Achenes ellipsoid, 1.4-1.6 × 0.7-0.9 mm.

Fruiting summer. Sedge meadows, moist shores; 10-300 m; Greenland; Man., Nfld. and Labr., N.W.T., Nunavut, Ont., Que., Yukon; Alaska; Eurasia.

Carex atrofusca is the only species in sect. Aulocytsis with papillose perigynia, suggesting that it is perhaps misplaced.