135. Erigeron subtrinervis Rydberg ex Porter & Britton, Mem. Torrey Bot. Club. 5: 328. 1894.
Erigeron glabellus Nuttall var. mollis A. Gray, Proc. Acad. Nat. Sci. Philadelphia 15: 64. 1864, not E. mollis D. Don 1825; E. speciosus (Lindley) de Candolle var. mollis (A. Gray) S. L. Welsh
Perennials, 15–90 cm; rhizomatous to subrhizomatous, fibrous-rooted, caudices usually branched, woody, thick. Stems erect, moderately to densely hirsute (hairs 0.5–0.8 mm), eglandular. Leaves basal (usually withering by flowering) and cauline; basal blades oblanceolate-spatulate, 30–80 × 6–20(–27) mm, margins entire, faces evenly hirsute to strigoso-hirsute, usually eglandular; cauline blades lanceolate to oblong, oblong-ovate, or broadly ovate, nearly even-sized distally or sometimes mid largest (continuing to immediately proximal to heads, bases clasping to subclasping). Heads 1–6(–21) in corymbiform arrays. Involucres 6–9 × 13–20 mm. Phyllaries in 2–3(–4) series, moderately to densely hirsute, minutely glandular. Ray florets 100–150; corollas blue to lavender, 7–18 mm (ca. 1 mm wide), laminae coiling at tips. Disc corollas 4–5 mm. Cypselae 1.6–2 mm, 2(–4)-nerved, faces sparsely strigose; pappi: outer of setae, inner of 20–30 bristles.
Flowering (Jun–)Jul–Sep. Opening and margins, roadsides, often shaded, ponderosa pine, pine-fir, mixed conifer, aspen; 1800–3000(–3500) m; Colo., Idaho, Mont., Nebr., N.Mex., N.Dak., S.Dak., Utah, Wyo.
Erigeron subtrinervis is variable in vestiture, perhaps reflecting gene exchange with E. speciosus. Erigeron speciosus var. mollis (A. Gray) S. L. Welsh may be a recurrent hybrid; it is identified here within E. subtrinervis.