Euphorbia, also commonly called "Spurge" is one of the largest genera of flowering plants.  Spurge can have some similarities to cactus in regards to shape and the ability to go through droughts although they are not cactus. They have a simplified bloom with no petals. It Is more of the shape of the Euphorbia's body that people go crazy over this Genus as they are indeed known for their architecture. The  Euphorbia obesa, also called "Baseball Plant", has a ball shaped segmented body that eventually turns cylindrical with age. Balls.

Images are used for general reference only. The size, bloom state, flower color and shape of each plant will vary.