Publication: Trans. Amer. Philos. Soc. n. s. 11: 175. 1860.
selected vouchers: WTU
Notes: FNA5: "Variety purpureum is the most widespread and common expression of the species, being found in southern British Columbia and southwestern Alberta, and in northern Arizona, eastern California, western Colorado, Idaho, western Montana, Nevada, northwestern New Mexico, eastern Oregon, Utah, southeastern Washington, and Wyoming. It approaches var. depressum both geographically and morphologically in the Yellowstone National Park area, and a clear distinction is not always possible. The name var. ovalifolium was long misapplied to what is here termed var. purpureum."