Euphorbia marginata (commonly known as snow-on-the-mountain, smoke-on-the-prairie, variegated spurge, or whitemargined spurge) is a small annual in the spurge family. It is native to parts of temperate North America, from Eastern Canada to the Southwestern United States. It is naturalized throughout much of China. The type specimen was collected in Rosebud County, Montana from the area of the Yellowstone River by William Clark during the Lewis and Clark Expedition.