Arnica sororia is a North American species of flowering plant known by the common name twin arnica.Calflora taxon report, University of California, Arnica sororia E. Greene, twin arnica It is native to Western Canada (British Columbia, Alberta, Saskatchewan) and the Western United States (Washington, Oregon, California, Nevada, Utah, Idaho, Montana, Wyoming, South Dakota).Biota of North America Program 2014 county distribution map It grows in grasslands and in conifer forests,Flora of North America Vol. 21 Page 370 Twin arnica Arnica sororia Greene as well as the sagebrush steppe.
Arnica sororia is a rhizomatous perennial herb producing one or more hairy, glandular stems tall. There are a few to several pairs of broadly lance-shaped leaves along the stem, the lower ones borne on petioles. Leaves may reach up to 14 cm long.Greene, Edward Lee 1910. Ottawa Naturalist 23(12): 213
The inflorescence consists of a daisy-like flower head, rarely more than one per stem. These are lined with phyllaries coated in glandular hairs. The flower head has a center of glandular yellow disc florets and a fringe of yellow ray florets. The fruit is an achene a few millimeters long with a white pappus.
References
External links Jepson Manual Treatment United States Department of Agriculture Plants Profile Calphotos Photo gallery, University of California