Plants densely cespitose; rhizomes ascending to erect, reddish brown, 0-5 mm, stout. Culms 3-7.5(-18) cm, scabrous distally; bases (remnants of old leaves) weakly to strongly fibrous. Leaf blades pale green, greatly exceeding culms, 1-2.3(-3.8) mm wide, herbaceous, glabrous abaxially, strongly scabrous to papillose adaxially. Inflorescences with both staminate and proximal spikes; peduncles of basal spikes erect, short to elongate, slender; peduncle of staminate spikes 0.7-5.2(-12.3) mm; proximal nonbasal bracts scalelike, usually shorter than (occasionally equaling) inflorescences. Spikes: proximal pistillate spikes 2-5 (basal spikes 1-3); cauline spikes overlapping with staminate spikes, with (1-)4-12 perigynia; staminate spikes 4.6-13 × 0.7-2.2 mm. Scales: pistillate scales reddish brown with narrow white margins, ovate, 2.8-3.9 × 1.5-1.9 mm, equaling or exceeding perigynia, apex acute to acuminate; staminate scales ovate to lanceolate, 3.5-5.1 × 1.1-2.2 mm, apex obtuse to acute. Anthers 1.7-2.2 mm. Perigynia pale green to pale brown, veinless, obovoid to globose, rarely ellipsoid, obtusely trigonous in cross section, 2.2-3.2 × 1-1.4 mm; beak straight, pale green to pale brown, strongly 2-edged, 0.4-1 mm, weakly ciliate-serrulate, apical teeth 0.1-0.2 mm. Stigmas 3. Achenes brown, ellipsoid, obtusely trigonous in cross section, 1.4-1.7 × 1-1.3 mm. 2n = 30, 32. Fruiting mid Mar-mid Jul. Open, dry to mesic, circumneutral to calcareous, clayey, sandy, and rocky fields, pastures, tall-grass prairies, glades, ridges, slopes, bluffs, dunes, barrens, open deciduous and mixed woodlands, also on serpentine and basalt, often at edges of ant hills; 90-300 m; Greenland; B.C., N.B., Nfld. and Labr., N.S., Ont., P.E.I., Que., Sask.; Ala., Ark., Ga., Ill., Ind., Kans., Ky., Maine, Md., Mass., Mich., Minn., Miss., Mo., Nebr., N.J., N.Y., N.C., Ohio, Okla., Pa., R.I., Tex., W.Va., Wis. Some botanists think Carex microrhyncha should be retained as a distinct species. A revision of the C. umbellata-C. tonsa complex may reveal distinctions; until that work is done, we prefer to combine C. microrhyncha with C. umbellata.
