Euphorbia marginata, snow-on-the-mountain, smoke-on-the-prairie, variegated spurge,
whitemargined spurge, is a small shrub

Shrub

A shrub or bush is distinguished from a tree by its multiple stems and shorter height, usually under 5–6 m tall. A large number of plants may become either shrubs or trees, depending on the growing conditions they experience...

 in the Euphorbiaceae

Euphorbiaceae

Euphorbiaceae, the Spurge family are a large family of flowering plants with 300 genera and around 7,500 species. Most are herbs, but some, especially in the tropics, are also shrubs or trees. Some are succulent and resemble cacti....

 or spurge family native to parts of temperate North America

North America

North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...

. The plant has grey-green leaves along branches and smaller leaves in terminal whorls with edges trimmed with wide white bands, creating, together with the white flowers, the appearance that gives the plant its common names. The type specimen

Biological type

In biology, a type is one particular specimen of an organism to which the scientific name of that organism is formally attached...

 was collected in Rosebud County, Montana

Rosebud County, Montana

-Demographics:As of the census of 2000, there were 9,383 people, 3,307 households, and 2,417 families residing in the county. The population density was 2 people per square mile . There were 3,912 housing units at an average density of 1 per square mile...

 from the area of the Yellowstone River

Yellowstone River

The Yellowstone River is a tributary of the Missouri River, approximately long, in the western United States. Considered the principal tributary of the upper Missouri, the river and its tributaries drain a wide area stretching from the Rocky Mountains in the vicinity of the Yellowstone National...

 by William Clark during the Lewis and Clark Expedition

Lewis and Clark Expedition

The Lewis and Clark Expedition, or ″Corps of Discovery Expedition" was the first transcontinental expedition to the Pacific Coast by the United States. Commissioned by President Thomas Jefferson and led by two Virginia-born veterans of Indian wars in the Ohio Valley, Meriwether Lewis and William...

.