Euphorbia horrida, the African milk barrel, or horrid spurge, is a species of flowering plant in the family Euphorbiaceae, native to South Africa. It is a cactus-like shrub showing remarkable similarities to the true cacti of the New World, and thus an example of convergent evolution. Growing to , it has blue-green, heavily ridged spiny stems carrying solitary green flowers in summer. In temperate regions it must be grown in heated conditions under glass, or as a houseplant on a sunny windowsill. It develops new shoots laterally at the base of the plant offset, often forming roots and thus a successful means of propagation. The main body of the plant appears blue-grey due to the epiticular wax, which protects it from harsh sun.
Euphorbia horrida is found in arid deserts in the southeastern cape of Africa. It is found in sandy, gravely soils that remain dry for most of the year. When it does rain, Euphorbia horrida rapidly absorbs water, expanding the ribs and swelling into a rotund, cylindrical shape.
When damaged, Euphorbia horrida rapidly releases a white sap, like of most plants in the Euphorbia genus. The sap is toxic, and causes eye and skin irritation. Left to dry, the sap becomes a sticky, clear, and hard-to-remove resin that remains toxic.