The photo above illustrates the ray and disk flowers of streambank arnica as seen from Little Pine Creek along the Canyon Mountain Trail #218, Strawberry Mountain Wilderness.........August 19, 2011.
Streambank arnica is also known as clasping arnica. Former variety piperi is also known as Columbia Gorge arnica.
It is a fairly attractive perennial with several to many upright stems arising from 30-80 cm high from freely rooting rhizomes. The herbage of the stems is more or less hairy and glandular. The stems are noticeably leafy with 5-12 pairs of opposite leaves which are relatively the same size along the whole stem. Individual leaves are narrowly lance-elliptic to lance-ovate in shape with either short petioles on the lower leaves to lacking petioles on the upper leaves. The leaves range from 5-12 cm long and 1.2-6 cm wide and have toothed margins (See photos below.). There are several bell-shaped heads with the involucral bracts (seen at right) narrowly lanceolate with acute to acuminate tips covered with sparse hairs or glandular hairs. The 8-14 yellow rays are 1-2 cm long and surround a yellow central disk.
Variety amplexicaulis: Has thinner leaves (up to 4 cm wide). Found in the range of the species which includes the Columbia River Gorge.
Variety piperi: Has thicker leaves (up to 6-8 cm wide). Found only in the Columbia River Gorge.
Streambank arnica is found in wet meadows, along streambanks, and in the spray zone around waterfalls.
Variety amplexicaulis may be found from Alaska south to northern California and east to western Montana.