Spearleaf arnica

Arnica longifolia subsp. myriadenia (Piper) Maguire; A. myriadenia Piper

Plants 30–60(–110) cm. Stems (often relatively numerous, clustered in clonal patches) simple. Leaves 5–7 pairs, mostly cauline (basal leaves usually withered by flowering); sessile or subsessile (proximalmost with connate-sheathing bases); blades lanceolate to lance-elliptic, 5–12(–15) × 1.5–3.5 cm, margins usually entire, rarely denticulate, apices acute to acuminate, faces scabrid-puberulent, sometimes glandular (distal leaves not much reduced). Heads 3–20(–35). Involucres turbinate-campanulate. Phyllaries 11–15(–20), narrow to broadly lanceolate. Ray florets 6–15; corollas yellow. Disc florets 6–11; corollas yellow; anthers yellow. Cypselae brown to black, 3–7 mm, glabrous or sparsely hirsutulous, stipitate-glandular; pappi stramineous to tawny, bristles barbellate to subplumose. 2n = 57, 76.

Flowering Jun–Oct. Montane coniferous forests to alpine, usually moist areas, stream banks or late snow-melt areas; 1300–3700 m; Alta., B.C.; Calif., Colo., Idaho, Mont., Nev., Oreg., Utah, Wash., Wyo.