Perennials 50-150(-200) cm, colonial; long-rhizomatous. Stems 1-5, ascending to erect, sparsely hispid distally. Leaves thin, mar­gins entire to serrate, apices acute, faces scabrous; basal withering by flowering, petiolate, blades elliptic to obovate 30-300 × 15-50 mm, attenuate, margins entire to serrate, apices acute, faces rough-hispidulous; proximalmost cauline sometimes withering by flowering, sessile, blades elliptic to obovate, 100-200 × 20-50 mm, bases rounded to ± clasping, sometimes auriculate, apices acute; distal sessile, blades 20-150 × 10-40 mm, bases cuneate, usually auriculate, apices acute. Heads in paniculiform arrays, branches 10-30 cm. Peduncles sparsely hairy, bracts lanceolate to linear. Involucres campanulate, 5-8 mm. Phyllaries in 4-6 series, narrowly oblong (outer) to linear (inner), unequal to subequal, bases scarious, margins scarious, entire, green zones lanceolate to narrowly elliptic, apices acute, faces glabrate or puberulent. Ray florets 15-40; corollas violet, laminae 8-15 × 1-2 mm. Disc florets 35-60+; corollas yellow, 3.5-4 mm, lobes triangular, 0.5-0.8 mm. Cypselae brown, cylindric to obovoid, not compressed, 2.5-3.5 mm, 3-4-nerved, faces hairy; pappi white, 3. 5-4 mm. 2n = 16.

Flowering Aug. Damp places in chaparral canyons; of conservation concern; 500-1500 m; Calif.

Symphyotrichum greatae is known from the south slopes of the San Gabriel Mountains.