Scirpus expansus Fernald

Plants spreading; rhizomes reddish, long, with conspicuous nodes and internodes. Culms: fertile ones upright or nearly so; nodes without axillary bulblets. Leaves 5–8 per culm; sheaths of proximal leaves red; proximal sheaths and blades with septa many, conspicuous; blades 30–68 cm × 9–23 mm. Inflorescences terminal; rays divaricate or occasionally ascending, proximal branches scabrellous (rarely smooth), distal branches scabrous, rays without axillary bulblets; bases of involucral bracts green or reddish, not glutinous. Spikelets in dense clusters of (1–)3–13(–24), (largest cluster with 7 or more), spikelets sessile, ovoid or narrowly ovoid, 2–6 × 1–3 mm; scales black with green midribs, ovate or broadly rounded-ovate to nearly triangular or broadly triangular, 1–2.2 mm, apex rounded to mucronate, mucro (if present) to 0.2 mm. Flowers: perianth bristles brittle-based, readily detached from achene, 6, stout, straight or curved, shorter than to 1.5 times as long as achene, with retrorse, thick-walled, sharp-pointed teeth densely arranged almost to base, at maturity projecting beyond scales; styles 3-fid. Achenes pale brown, oblong-elliptic to broadly elliptic or obovate in outline, plano-convex or sometimes plumply trigonous, 1–1.6 × (0.6–)0.8–1 mm. 2n = 64.