Threenerve Fleabane

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.

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.

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

Erigeron subtrinervis, called the three-nerved daisy, the three-nerve fleabane, or the hairy showy daisy, is a North American species of flowering plants in the family Asteraceae. It grows in various mountains of western Canada and the western United States: Rocky Mountains, northern Cascades, Black Hills, etc., from British Columbia and Washington state east to North Dakota and south as far as New Mexico.

Erigeron subtrinervis grows in openings and along roadsides in aspen groves and conifer forests, as well as on ridges and mountain peaks at high elevations. It is a perennial herb up to 90 cm (3 feet) tall, producing underground rhizomes and a woody caudex. The inflorescence generally contains 1-21 flower heads per stem, in a flat-topped array. Each head contains 100–150 purple or lavender ray florets surrounding many yellow disc florets.