Hairy arnica (Arnica mollis) is a native perennial growing from rhizomes. It can be found in moist meadows and open forests at mid to high elevations throughout Western United States and Western Canada.
This member of the aster family has solitary stems, which are sometimes branched near the flower heads. Also commonly called soft arnica, hairy arnica grows from 1/2′ to 2′ in height.
The plant has basal leaves which often turn color or fall by the time of flowering. The stem leaves are opposite, paired, lance-shaped to elliptical, hairy, and are entire or lightly toothed. The stem leaves lack petioles (stalks) and clasp the stem.
The 12 to 20 ray flowers are yellow and toothed at the top. The disk flowers are also yellow. The involucre surrounding the hairy arnica flower head is composed of hairy, lance-shaped bracts.
Hairy arnica fruits are achenes (small, dry, one-seeded) with white or slightly brownish pappus hairs at the top.
Arnica species, taken internally, cause a rise in body temperature. Externally applied they are antiseptic.
These hairy arnica plants are growing along the Kings Creek Trail in Lassen Volcanic National Park (CA).