Wolf’s spike-rush

Scirpus wolfii A. Gray, Proc. Amer. Acad. Arts 10: 77. 1874

Plants perennial, often forming large mats; rhizomes 0.25–0.6 mm thick, internodes 1–4 cm, scales 2 mm. Culms sometimes decumbent, in same plant sides variably smooth or with 1 to few acute ridges (often nearly smooth or with 1 ridge on 1 side and several ridges on the other), greatly compressed, usually inrolled when dry, rectangular in cross section, 10–40 cm × 0.3–1.5 mm, 0.2–0.5 mm thick, firm, margins often sharply acute, margins and often 1 or more ridges minutely serrulate at 20–30X. Leaves: distal leaf sheaths persistent, red proximally, colorless or stramineous or whitish distally, slightly inflated, thickly membranous, apex acute. Spikelets ovoid or lanceoloid, 3–9 × 1.5–2.5 mm, apex acute; floral scales 15–30, 6 per mm of rachilla, orange-brown or often stramineous or colorless, midrib region stramineous or greenish, ovate-lanceolate, (2.2–)2.7–3.2 × 1.5 mm, midrib prominent, apex acute. Flowers: perianth bristles absent; anthers 1.1–1.75 mm. Achenes compressed-trigonous, with angles plus longitudinal ridges ca. 9–13, prominent, obovoid, mostly 2 times longer than wide, 0.7–0.9(–1.1) × (0.4–)0.5 mm, trabeculae 30–60, rather obscure and crowded. Tubercles brownish, pyramidal, usually depressed, 0.1–0.15 × 0.2–0.25 mm.

Fruiting late spring–early summer (May–Jun). Ephemeral pools in open grasslands, oak woodlands on river terraces, limestone barrens; 10–500 m; Ala., Ark., Colo., Ill., Ind., Iowa, Kans., La., Minn., Miss., Mo., N.Y., N.Dak., Ohio, Okla., Tenn., Tex., Wis.

Eleocharis wolfii is presumably extirpated from Colorado, Kansas, New York (Long Island), and Ohio. It was recently rediscovered in Wisconsin. Some literature reports (e.g. from the Great Plains) are based on misidentified specimens. I have not seen specimens to verify literature reports from Alberta, Saskatchewan, Colorado, Missouri, and Nebraska.