Polygala senega is a species of flowering plant in the milkwort family, Polygalaceae. It is native to North America, where it is distributed in southern Canada and the central and eastern United States. Its common names include Seneca snakeroot, senega snakeroot, senegaroot, rattlesnake root, and mountain flax. Its species name honors the Seneca people, a Native American group who used the plant to treat snakebite.