Plants usually with sterile culms; usually cespitose, often with rhizomes 2-15 cm long, 1-3 mm thick. Culms (30) 55-80 (100) cm, unbranched, scabrous beneath the panicles; nodes (1) 2 (5). Sheaths and collars usually scabrous, rarely smooth; ligules (0.5) 2-5.5 (7) mm, usually truncate, entire to slightly lacerate; blades (8) 10-20 (27) cm long, (1.5) 2-3 (4) mm wide, usually involute, abaxial surfaces usually scabrous, rarely smooth, adaxial surfaces scabrous, glabrous or sparsely hairy, both surfaces with abundant white glands between the veins, visible only with magnification. Panicles (6) 8-11 (15) cm long, (1) 1.2-1.5 cm wide, contracted, mostly erect, pale green to green; branches 2-4 (4.5) cm, scabridulous, usually spikelet-bearing to the base. Spikelets (4.5) 5-7 (8) mm; rachilla prolongations about 1.5 mm, hairs 1-2 mm. Glumes keeled, usually scabrous over the entire surface, rarely only the keels scabrous distally, lateral-veins prominent, apices acute to acuminate; callus hairs 1-1.5 (2) mm, 0.2-0.4 times as long as the lemmas, sparse; lemmas 4.5-6.5 mm, 0-2 mm shorter than the glumes; awns 5-6 (8) mm, attached to the lower 1/10 – 1/5 of the lemmas, exserted less than 2 mm, stout, distinguishable from the callus hairs, bent; anthers (2.5) 3-3.5 (4) mm. 2n = 28.
Calamagrostis ophitidis grows in meadows, seeps, grasslands, and chaparral, as well as in coniferous forests, on serpentine outcrops and soils, at 50-1100 m. It is known only from Sonoma, Marin, Mendocino, Lake, and Napa counties in California.
"decumbent" is not a number.