Fimbristylis thermalis S. Watson

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.

Ariz., Calif., Nev., Utah; Mexico (Baja California, Coahuila).

Fruiting spring–fall.

Mineralized sands of hot springs, alkaline seep meadows; 300–600m.

Fimbristylis thermalis is a species of fimbry known by the common name hot springs fimbry. It is native to the southwestern United States and northern Mexico. It has been reported from Baja California, California, Arizona, Nevada, Utah and Coahuila.

Fimbristylis thermalis grows in alkaline mud and sand, especially around hot springs and mineral-rich seeps. This is a thick-stemmed sedge which grows singly or in clumps and reaches maximum heights over a meter. It has a long rhizome system. It has short, flat, spiral-arranged leaves. At the top of the stem is an inflorescence of ovate, pointed spikelets, each on a long peduncle. The spikelet has many hairy bracts. The fruit is a shiny brown achene one to two millimeters long.

Fimbristylis thermalis là loài thực vật có hoa trong họ Cói. Loài này được S.Watson mô tả khoa học đầu tiên năm 1871.