Cirsium drummondii is widely distributed across Canada from the Northwest Territories to British Columbia and Ontario. The name C. drummondii has been misapplied to a wide range of plants across the western United States that are now treated as one or another variety of the polymorphic C. scariosum. The only documented modern occurrences of C. drummondii in the United States are in the Black Hills of South Dakota and adjacent Wyoming. Specimens collected by Hall and Harbour (342) are the only ones of C. drummondii known from Colorado. Somewhat similar plants from northern Nevada are treated here as C. scariosum var. toiyabense. During Pleistocene glaciations the ancestors of C. drummondii undoubtedly occupied a more southerly distribution and very likely came into direct contact with populations of C. scariosum. The observed similarities between C. drummondii and C. scariosum var. toiyabense are probably a relict of that ancient contact.