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.
Phenology: Flowering Jul–Aug.
Habitat: Salt marshes, wet grasslands
Elevation: 0–200 m
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.
of conservation concern