Cirsium horridulum, called bristly thistle, horrid thistle, yellow thistle or bull thistle, is a North American species of plants in the thistle tribe within the sunflower family. The species is native to the eastern and southern United States from New England to Florida, Texas, and Oklahoma as well as to Mexico, Belize, Guatemala, Honduras, and the Bahamas. Thomas Nuttall (1786-1859) described var. megacanthum as "one of the most terribly armed plants in the genus."