Euphorbia horrida, the African milk barrel, 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 1.5 meters, 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.
 
Here we have the variegated versions.
 
Size guide:
Mini - 6cm 
Small - 8cm 
Medium - 10cm
Large - 13cm
Extra Large - 15 cm