Culms aphyllopodic, without dead leaf remains at base, 20–70 cm. Leaf blades 2–5 mm wide, margins revolute, scabrous at tip. Inflorescences: proximal bracts 4–11 cm, shorter to longer than inflorescences; lateral spikes 10–30 × 6–8 mm, with 15–40 perigynia; terminal spikes 12–32 × 3–8 mm. Pistillate scales lanceolate, 3–7.5(–9) × 1.6–2.5 mm, narrower that, longer than perigynia, awn to 2–12 mm. Staminate scales oblong-obovate, 4.5–6 × 1.3–2.4 mm, apex bifid to emarginate, at least proximal scales with awn 2–6 mm. Anthers 3.3–5 mm. Perigynia 3.8–6.8 × 1.7–2.3 mm, apex tapering and rounded; beak 0.1–0.3 mm. 2n = 60.

Fruiting summer. Marshes, shores, and other wet open places; 0–1000 m; B.C., Yukon; Alaska, Oreg., Wash.; coastal Asia.

T. V. Egorova (1999) included Carex macrochaeta in sect. Scitae. The species commonly has a white or cream tomentum on many roots, although most individuals have at least some roots with a yellowish tomentum. The sectional placement of this species requires further investigation.