161. Carex opaca (F. J. Hermann) P. E. Rothrock & Reznicek, Novon. 11: 223. 2001.
Carex bicknellii Britton var. opaca F. J. Hermann, Sida 5: 49. 1972
Plants densely cespitose, to 200 culms together; rhizomes appearing elongate only in old clumps. Culms 50–115 cm; vegetative culms few, inconspicuous, usually fewer than 12 leaves, not strikingly 3-ranked. Leaves: sheaths glabrous, hyaline sometimes brown tinged band near collar, the summits U-shaped to truncate, ± equaling the base of the blade; distal ligules 1.5–5.4 mm; blades 3–6 per fertile culm, 3.5–40 cm × 1.5–4.6 mm. Inflorescences open, erect to slightly arching, pale or golden brown, 2.4–5.5(–6.4) cm × 6.5–21 mm; proximal internode 4–13(–18) mm; 2d internode 3–11 mm; proximal bracts scalelike, with bristle tips to 1.5 cm. Spikes 4–8(–10), distinct, ovoid, 10–22 × 4–11 mm, base rounded to tapered, apex rounded to acute. Pistillate scales pale brown with narrow yellow-green to brown midstripe, lanceolate to narrowly ovate, (3.6–)3.9–5 mm, 2.4–3.1(–3.4) times as long as wide, barely or not reaching base of perigynium beaks, margin hyaline, apex firm and herbaceous, flat or inrolled, obtuse to acute. Staminate scales obtuse to acuminate. Anthers (1.8–)2.2–3.6 mm. Perigynia 15–80 in larger spikes, ± appressed, yellowish green to brown with paler margins, conspicuously 3–7-veined adaxially, 8–12-veined abaxially, 2–5 veins in wings, broadly ovate, broadly elliptic, or orbiculate, often strongly concave, (5.6–)6–7.1 × 3.3–4.6(–4.8) mm, 0.5–0.7 mm thick, margin flat, including wing 0.6–1.3 mm wide, smooth; beak pale or golden brown at tip, strongly flattened, (1.2–)1.5–2.1(–2.3) mm, serrulate-margined to apex, abaxial suture yellow-green to copper-brown, distance from tip of beak to achene 2.8–4 mm. Achenes broadly ovate to oblong, 1.8–2.4 × 1.3–1.9 mm, 0.5–0.7 mm thick, apiculum to 0.5–1.1 mm. 2n = 66, 68.
Fruiting early summer. Low areas in prairies, roadside ditches, poorly drained sites; 50–400 m; Ark., Ill., Kans., Miss., Mo., Okla.