Northern Prairie Wildlife Research Center
Only western North Dakota is home to the Colorado rubber plant. Except for one record in Divide County, all collections of this species have been south and west of the Missouri River. Elsewhere, the plant occurs south along the east side of the Rocky Mountains from Saskatchewan to Texas west to Utah and Arizona at elevations up to 10,000 ft.
North Dakota specimens of Colorado rubber plant are about 4 inches tall. Plants are perennial, and tufted from a branching woody structure (caudex) atop a rather thin taproot. The thread-like leaves are branched, lie below the flower heads, and are covered with tiny resin glands. Mature plants usually have about 5-20 stems that each have 1-5 yellow flower heads about 3/4-inch wide. Fruits are tiny achenes about 1/8-inch long.
Look for Colorado rubber plant from June to August on dry soils in hilly areas. Grazing seems to have little effect on the plant's abundance. These "rubber plants" probably were so called because the Amerindians of New Mexico made chewing gum from the bark and roots.
Colorado rubber plant is a member of the sunflower family (Asteraceae) of which there are about 15,000 species worldwide and about 200 species in North Dakota. The generic name was compounded from the Greek humen "membrane" and oxys "sour", likely in allusion to the translucent scales at the base of the flowers and the sour or bitter taste of several of the species. Theodore Cockerell (1866-1948) published the first acceptable scientific description of the plant in 1904, long after its discovery by Sir William Jackson Hooker (1785-1865), who named the species in honor of the famous Scottish biologist and arctic explorer Sir John Richardson (1787-1865). Professor Cockerell was an intrepid student of the natural history of Colorado and New Mexico.