Marshes, swales, and wet meadows; moist forests and clearings.

Some specimens of C. sparganioides and C. cephaloidea might seem to run here in the key. They would differ from C. alopecoidea in nearly always lacking purplish dots on the sheaths, in having generally wider leaves (especially C. sparganioides), in the shorter beak of the perigynium (not over about half as long as the body), in their pistillate scales barely or not at all reaching the bases of the beaks of the perigynia they subtend, and in their much shorter anthers. Neither will have the stout, very sharply angled culms typical of Carex alopecoidea.