Luc Brouillet, John C. Semple, Geraldine A. Allen, Kenton L. Chambers, Scott D. Sundberg+ in Flora of North America (vol. 20)
Perennials, 20-80 cm, colonial; long-rhizomatous. Stems 1-5+, ascending to erect, glabrous or sparsely puberulent. Leaves thin, margins entire, apices acute, faces glabrous or sparsely puberulent; basal persistent, petiolate, blades narrowly elliptic to obovate, 50-150 × 3-15 mm, attenuate, margins entire; proximal cauline sessile or subpetiolate, blades linear to narrowly elliptic, 50-150 × 2-15 mm, bases attenuate or cuneate; distal sessile, blades 30-60 × 2-10 mm, reduced distally, bases cuneate to rounded. Heads in corymbiform to paniculiform arrays, branches usually few. Peduncles sparsely hairy, bracts 0-3+. Involucres campanulate, 5-10 mm. Phyllaries in 3-5 series, narrowly oblong or linear (outer) to linear (inner), unequal, bases indurate, margins entire, green zones elliptic to lanceolate , apices usually acute, sometimes obtuse, faces glabrous or ± puberulent. Ray florets 15-40; corollas violet, laminae 9-15 × 1-2 mm. Disc florets 30-80(-100); corollas yellow, sometimes becoming reddish, 4.5-6 mm, lobes triangular, 0.5-1 mm. Cypselae brown, cylindric to obovoid, not compressed, 2.5-3.5 mm, ± 4-nerved, faces hairy; pappi whitish, 5-7 mm. Symphyotrichum spathulatum is a variable species, widespread in montane regions of western North America. It hybridizes with S. eatonii, S. foliaceum, and S. hendersonii.