10.
Arnica rydbergii
Greene, Pittonia. 4: 36. 1899.
Rydberg's arnica
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
. 2
n
= 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.
