Carex agglomerata Mackenzie, Bull. Torrey Bot. Club 33: 442. 1906, not C. B. Clarke 1903; C. sparganioides Muhlenberg ex Willdenow var. aggregata (Mackenzie) Gleason

Plants without conspicuous rhizomes. Culms (20–)30–100 cm, 1.5–3.5 mm wide basally, 0.7–1.2 mm wide distally. Leaves: sheaths usually loose, proximal green-and-white-striped and green-and-white-mottled, with conspicous transverse veins on back, fronts white to hyaline, sometimes red dotted and transversely rugose, yellow or brown and thickened at mouth; ligules 1–4.5 mm, shorter than to as long as wide; widest leaf blades 3.5–5 mm wide. Inflorescences with 5–10 spikes, (1.5–)2–5 cm × 8–13 mm; proximal internodes shorter than to as long as proximal spikes; proximal bracts to 3 cm; spikes with 5–15 ascending to spreading perigynia. Pistillate scales hyaline or pale brown with green, 1–3-veined center, ovate, 2.2–3.5 × 1.2–1.8 mm, body 2/3 as long to almost length of perigynia, apex acuminate to short-awned. Anthers 1.5–2.5 mm. Perigynia pale green to pale brown, veinless or weakly 2–5-veined abaxially, 3.4–4.6 × 1.9–2.8 mm, body somewhat spongy, thickened at base, margins serrulate distally; beak 0.7–1.4 mm, apical teeth 0.3–1 mm. Achenes circular to elliptic-circular, 1.8–2.1 × 1.6–1.8 mm.

Fruiting late spring. Meadows, thickets, open forests, usually on calcareous soils; 50–300 m; Ont.; Ala., Del., D.C., Ill., Ind., Iowa, Ky., Md., Minn., Mo., N.J., N.Y., N.C., Ohio, Okla., Pa., S.Dak., Tenn., Va., W.Va., Wis.

Carex aggregata may be difficult to distinguish from C. gravida if the leaf sheaths are damaged or not visible on specimens.