Arnica longifolia is a North American species of arnica in the sunflower family, known by the common names seep-spring arnica, longleaf arnica and spearleaf arnica. This flowering perennial is native to the forests of western Canada (British Columbia + Alberta) and the western United States (Rocky Mountains, Cascades, Coast Ranges, Sierra Nevada and other mountains of California, Oregon, Washington, Idaho, Nevada, Utah, Wyoming, Colorado, and Montana).
Arnica longifolia is a rhizomatous plant forming large bunching patches of groundcover in moist, cool areas. The foliage is rough, mint-green, and sometimes sticky with glandular secretions. The stems are erect and bear daisylike flower heads with a diameter of 2 cm, with deep yellow ray florets and yellow to reddish or orange disc florets. The fruit is a reddish achene with a small pappus.