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.
Phenology: Fruiting summer.
Habitat: Sedge meadows, moist shores
Elevation: 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.