Plants 1–5 dm; rhizomatous.
Stems simple, densely glandular-puberulent, setulose distally.
Basal leaves well developed; petioles winged.
Cauline leaves 1–3 pairs, much reduced distally; blades oblanceolate or lance-elliptic to linear, 2.5–8 cm, proximal bases woolly-tufted, margins entire, veins parallel from bases, tips acute, surfaces minutely stipitate-glandular, often gland-dotted; sessile.
Heads radiate.
Peduncles densely glandular-puberulent.
Involucres hemispheric, 10–16 mm.
Phyllaries elliptic-oblong to broadly lanceolate, tips acute or obtuse, surfaces densely stipitate-glandular, setulose.
Ray florets 8–16; rays 12–30 mm, orange-yellow.
Disc florets 15–60; corollas 7–10 mm, yellow, with glandular and non-glandular trichomes.
Fruits columnar-fusiform, 4–7 mm, gray or blackish, densely hirsute; pappus bristles 5–7 mm, white or straw-colored, barbellate.
2n=38, 57.
Moist meadows, open woodlands. Flowering Jun–Aug. 1600–2800 m. BR, BW, Casc, ECas. CA, NV, ID, WA; north to British Columbia, northeast to Manitoba, east to SD, southeast to NM. Native.
The disc corolla pubescence traits differing between Arnica fulgens and A. sororia may be difficult to see except under high magnification.
as described under Arnica fulgens
Plants 10-75 cm. Stems solitary, simple. Leaves 3-5 pairs, crowded toward stem bases (some or all axils with dense tufts of brown wool); petiolate (petioles at least basal leaves, narrow or broadly winged); blades (with 3 or 5 prom-inent, subparallel veins) usually narrowly oblanceolate to oblong, rarely oval or broadly spatulate, 4.5-20 × 0.5-2.5 cm, margins denticulate, apices obtuse, faces moderately uniformly hairy, stipitate-glandular. Heads 1(-3). Involucres broadly hemispheric. Phyllaries 13-21, elliptic-oblong or narrowly to broadly lanceolate. Ray florets 8-16; corollas yellow-orange. Disc florets: corollas yellow; anthers yellow. Cypselae brown, 3.5-7 mm, densely hirsute, sometimes sparingly stipitate-glandular; pappi usually white, sometimes tawny, bristles barbellate. 2n = 38, 57.Flowering May-Jul. Prairies and grasslands to montane conifer forests; 500-3000 m; Alta., B.C., Man., Sask.; Calif., Colo., Idaho, Mont., Nev., N.Dak., Oreg., S.Dak., Utah, Wash., Wyo.