Culms obtusely trigonous in cross section, 15–70 cm, smooth. Leaves: ligules 1.2–3 mm, wider than long; blades yellowish green, M-shaped to flat, widest leaves 1.6–3.5(–4.2) mm wide, smooth abaxially, minutely papillose adaxially, especially distally. Inflorescences 1.8–18 cm; bract sheaths with apex concave; proximal (1–)2–3(–4) spikes pistillate, distal spikes erect, aggregated or the proximal sometimes remote, ovoid. Pistillate scales narrowly ovate, mostly 1/3–2/3 length of perigynia, apex acute. Anthers 1.1–2.7 mm. Perigynia spreading or the proximal somewhat reflexed, yellowish green, 20–26-veined, essentially uninflated, lanceolate, 8.7–12.1 × 1.3–2.1 mm, 4–7 times as long as wide, apex tapered, bidentulate; beak absent. Achenes 2.2–3 × 1.2–1.7 mm.
Phenology: Fruiting late spring–summer.
Habitat: Bogs, fens, lakeshores, stream banks, open seeps, in sandy or peaty, often acidic soils
Elevation: 0–1000 m
St. Pierre and Miquelon, Man., N.B., Nfld. and Labr., N.S., Ont., Que., Sask., Maine, Md., Mass., Mich., Minn., N.H., N.Y., Vt., Wis.
Carex michauxiana is closely related to the east Asian C. dolichocarpa C. A. Meyer ex V. I. Kreczetowicz.