Perennials, 40-150(-200) cm, colonial; long-rhizomatous. Stems 1-5, ascending to erect, glabrous. Leaves thin, margins entire, apices acute, faces glabrous; basal withering by flowering, petiolate, blades linear to narrowly lanceolate, 100-150 × 5-10 mm, attenuate or cuneate, margins entire, apices acute, faces usually glabrous; proximalmost cauline usually withering by flowering, sessile, blades linear to narrowly lanceolate or oblanceolate, 50-90 × 5-8(-20) mm, bases attenuate or cuneate; distal sessile, blades 40-80 × 5-8(-15) mm, bases cuneate. Heads in paniculiform arrays, branches some at least 25 cm. Peduncles glabrous or sparsely villous, bracts 5-15, sessile, lance-linear to lanceolate, margins sometimes spiculate. Involucres campanulate, 5-8 mm. Phyllaries in 4-5 series, narrowly oblong (outer) to linear (inner), unequal (outer at least 3 times longer than wide), bases (outer) indurate ¹ / 2 or less, margins scarious proximally, eciliate or ciliolate, green zones lanceolate to elliptic, apices acute to acuminate, faces glabrous. Ray florets 20-45+; corollas violet, laminae 10-18 × 1-2 mm. Disc florets 35-70+; corollas yellow, 5-7 mm, lobes triangular, 0.8-1.5 mm. Cypselae brown, cylindric to obovoid, not compressed, 3-4 mm, 2-4-nerved, faces glabrous or hairy; pappi white, 5-7 mm. 2n = 16, 64.

Flowering Jul-Aug. Salt marshes, wet grasslands; 0-200 m; of conservation concern; Calif.

Symphyotrichum lentum is known only from the Sacramento Valley, North Bay County, lower Sacramento River, and San Francisco Bay areas. Probable intergrades with S. chilense have been noted.