Arnica rydbergii

Plants 8-35 cm. Stems (branches from rhizomes) simple. Leaves 2-4 pairs (basal often persistent on sterile rosettes), mostly cauline; petiolate (at least basal) or sessile; blades oblanceolate to spatulate, 2-7 × 0.5-2.5 cm, margins usually entire, sometimes denticulate, rarely dentate, apices usually acute, sometimes obtuse, faces sparsely puberulent, moderately pubescent distally, stipitate-glandular. Heads 1-3(-5). Involucres turbinate-campanulate. Phyllaries 9-15, linear-oblong to narrowly lanceolate. Ray florets 6-10; corollas yellow. Disc florets: corollas yellow; anthers yellow. Cypselae brown, 4-7 mm, densely hirsute (not stipitate-glandular); pappi white, bristles barbellate . 2n = 38, 76.

Flowering Jul-Aug. Dry to mesic, exposed, rocky alpine slopes and ridges or alpine meadows; 1200-3400 m; Alta., B.C.; Colo., Idaho, Mont., Oreg., Utah, Wash., Wyo.