2. Fimbristylis thermalis S. Watson, Botany (Fortieth Parallel). 360. 1871.
Plants perennial, robust, 50–150 cm, cespitose or with culms solitary; rhizomes scaly, slender, elongate. Leaves nearly distichous, spreading to ascending, 1/2 length of culms; sheath margins entire, backs smooth to pubescent; ligule present, complete; blades narrowly linear, proximally flat, 2–3.5(–4) mm wide, margins scabrid-ciliate, abaxial surface sometimes pubescent. Inflorescences: anthelae simple or compound, longer than wide; scapes wandlike, nearly terete or slightly compressed, distally 1 mm thick, marginal ribs scabrid; longest primary involucral bract shorter than panicle. Spikelets pale dull brown, lance-ovoid to cylindric-ellipsoid, 10–12 mm; fertile scales ovate, 3.5–4 mm, apex broadly acute, ciliate, surface uniformly puberulent, midrib excurrent as mucro or cusp. Flowers: stamens 3; styles 2-fid, flat, fimbriate. Achenes dark brown, lenticular-obovoid, 1.5 mm, finely cancellate, with 20 or more longitudinal rows of horizontally rectangular pits per side. 2n = 20.
Fruiting spring–fall. Mineralized sands of hot springs, alkaline seep meadows; 300–600 m; Ariz., Calif., Nev., Utah; Mexico (Baja California, Coahuila).