Northern Prairie Wildlife Research Center
The natural distribution of snow-on-the-mountain in North Dakota seems to be in counties along the west side of the Missouri River about up to Oliver County. However, a few plants have been collected, perhaps as escapes or accidental introductions, in Cass and Eddy Counties. Elsewhere, plants can be found from Minnesota to Montana south to Texas and New Mexico at elevations up to 7,000 feet. In other areas, plants have escaped from cultivation.
Snow-on-the-mountain is an annual herb with single, nearly smooth stems and milky juice. Unless damaged, plants are unbranched below the inflorescence. North Dakota specimens are usually less than two feet tall, but plants up to four feet in height are found farther south. The alternate, pale green leaves are up to three inches long and oval to nearly round. Small, white and green flowers are clustered atop the plant. The floral leaves and bracts are extremely conspicuous; their broad white-to-pink margins contrast nicely with green inner surfaces. At maturity, tiny capsules containing three seeds each, are formed.
Look for snow-on-the-mountain from June to October. Plants occur on a wide variety of soil types. In native prairie pastures, more plants are found where grazing is heavy or moderate, indicating that cattle probably avoid the plant and at the same time create bare areas for seeds to germinate.
Worldwide, Euphorbias are economically important plants used for medicines, rubbers, glues, paints, and other products. Some relatives, like leafy spurge (E.esula), have become highly noxious weeds when introduced to other countries. Snow-on-the-mountain forms a latex that was used for chewing by the Kiowa. The plant is often cultivated for ornament, and some early cattlemen used the plant's juice for branding cattle in preference to a hot iron. However, contact with the juice causes dermatitis in some people.
Snow-on-the-mountain is a member of the spurge family (Euphorbiaceae), the family and generic name honoring Euphorbus, physician of King Juba of Numidia. This family has about 7,000 species worldwide, including the economically important rubber trees, cassava, and tapioca. The specific epithet marginata was used because of the showy borders of the upper leaves and bracts. Snow-on-the-mountain was first described for science by the German botanist Frederick Pursh in his monumental Flora Americae Septentrionalis of 1814. Pursh was the first to publish on the many new plants collected by Lewis and Clark.