Phytologia 77: 293. 1995.
Perennials, 40–120 cm, colonial; long-rhizomatous. Stems 1–5+, ascending to erect, proximally glabrous, distally usually glabrous or sparsely puberulent, rarely densely hirsute. Leaves thin, margins entire or often serrate, apices acute, faces glabrous or sparsely puberulent; basal withering by flowering, petiolate to subpetiolate, blades oblanceolate to narrowly elliptic or linear, 50–150 × 3–25 mm, bases attenuate, margins entire or sometimes serrate, apices acute; proximalmost cauline withering by flowering, subpetiolate or sessile, blades obovate or oblanceolate to narrowly elliptic, rarely linear, 50–150 × 4–35 mm, bases attenuate or cuneate; distal sessile, blades 30–100 (–130) × 3–15 (–30) mm, bases cuneate, rounded or sometimes ± auriculate, margins sometimes serrate, scabrous. Heads in open, corymbiform, paniculiform, or racemiform arrays, branches 5–30 cm. Peduncles sparsely hairy, bracts 1–10, lance-oblong to linear, sometimes clasping, margins scabrous. Involucres campanulate, 5–8 (–10) mm. Phyllaries in 4–6 series, appressed or squarrose, oblong or narrowly oblanceolate or linear (outer) to linear (inner), unequal to subequal (outer shorter than or equal to inner, often less than 3 times as long as wide), bases outer indurate less than 1/2 (some foliaceous), inner scarious, margins entire, sometimes ciliate, green zones obovate to elliptic, apices acute to obtuse, faces usually glabrous, rarely sparsely puberulent. Ray-florets 15–45; corollas violet, laminae 10–16 (–20) × (1–) 1.5–2.5 mm. Disc-florets 50–75; corollas yellow becoming reddish, 4–7 mm, lobes triangular, 0.5–1 mm, glabrous. Cypselae brown or purplish, cylindric to obovoid, not compressed, 2–4 mm, 3–6-nerved, faces hairy; pappi whitish to tawny or reddish, 4.5–8 mm. 2n = 48, 64, 80, 96.
Phenology: Flowering Jul–Sep.
Habitat: Marshes, thickets, weedy meadows, open disturbed habitats
Elevation: 0–1000 m
Alta., B.C., Alaska, Calif., Idaho, Mont., Oreg., Wash.
Symphyotrichum subspicatum is a weedy, highly polyploid species, probably of allopolyploid derivation from different combinations of species including S. chilense, S. bracteolatum, S. foliaceum, S. laeve, and S. spathulatum. Hybrids with S. hallii are known from western Oregon. The species passes into S. foliaceum in southeastern Alaska.
"thin" is not a number.