Phytologia 77: 278. 1995.
Perennials, 40–100 cm, colonial or cespitose; long-rhizomatous. Stems 1–5+, ascending to erect, glabrous or puberulent. Leaves thin, margins entire, apices acute, faces glabrous or puberulent; basal often withering by flowering, petiolate, blades broadly elliptic to obovate, 5–200 × 10–35 mm, attenuate or cuneate, margins entire, apices acute; proximalmost cauline sometimes withering by flowering, sessile, blades oblanceolate to obovate, 70–120 × 15–50 mm, bases strongly clasping, enlarged and usually narrowed distally, usually prominently auriculate, margins entire, apices acute; distal sessile, blades lanceolate to broadly elliptic, 30–110 × 10–30 mm, bases truncate or auriculate, margins entire. Heads borne singly or in often congested, paniculiform arrays, branches 20–30 cm. Peduncles sparsely to densely cinereous, bracts lanceolate. Involucres campanulate, 10–20 mm. Phyllaries in 4–5 series, broadly to narrowly lanceolate or oblanceolate (outer) to linear (inner), ± equal or outer slightly exceeding inner, bases outer foliaceous, inner scarious, margins scarious, entire or erose, green zones elliptic to lanceolate, apices acute, faces glabrous or finely hairy. Ray-florets 25–55; corollas violet, laminae 10–18 × 1–2 mm. Disc-florets 60–150+; corollas yellow, 2.5–4 mm, lobes triangular, 0.4–0.5 mm. Cypselae brown, cylindric to obovoid, not compressed, 3–3.5 mm, 3–6-nerved, faces hairy; pappi white, 5–9 (–11) mm. 2n = 16, 32.
Phenology: Flowering Jul–Aug.
Habitat: Damp meadows in dry forests, often near springs and streams
Elevation: 1000–1500 m
Alta., Idaho, Mont., Oreg., Wash.
Symphyotrichum cusickii occurs principally in north-eastern Oregon, north-central Idaho, and adjacent western Montana.
"thin" is not a number.