387. Carex schweinitzii Dewey ex Schweinitz, Ann. Lyceum Nat. Hist. New York. 1: 71. 1824.
Carex de Schweinitz
Plants extensively colonial; rhizomes long. Culms trigonous in cross section, 18–65 cm, smooth distally. Leaves: basal sheaths pale brown; ligules as wide to wider than long; blades pale to mid green, flat to W-shaped, 4–11 mm wide, glabrous. Inflorescences 8–24 cm; proximal bract 11–37 cm, exceeding inflorescence; proximal 2–4 spikes pistillate, erect or often the proximal ascending to spreading; terminal 1(–2) spikes staminate. Pistillate scales lanceolate-acuminate, 2.4–6.9 × 0.3–0.9 mm, shorter than or the proximal longer than perigynia, margins serrulate-ciliate, apex with prominent scabrous awn. Staminate scales acute to acuminate, smooth except at tip. Perigynia ascending, 7–11-veined, narrowly elliptic, 4.2–7 × 1.3–1.8 mm, apex tapered; beak 1.4–2.4 mm, bidentulate, smooth, teeth straight, 0.2–0.5 mm. Stigmas 3. Achenes pale brown, trigonous, smooth.
Fruiting Jun–Jul. Shallow cold streams, springheads, seeps, margins of fens, and seepy stream, pond, and lakeshores in open or lightly shaded sites, in highly calcareous soils; 100–600 m; Ont.; Conn., Mass., Mich., Mo., N.Y., Pa., Vt., Va., Wis.
Carex schweinitzii is very local and uncommon but often forms large colonies where present. It hybridizes occasionally with C. hystericina. The single, old Missouri collection (G. Yatskievych 1999+) seems so far disjunct as to suggest that there may have been a label mixup.