This is the Euphorbia echinus from Africa. Even though it looks a lot like a cactus it is not. Cactus are indigenous to the Americas. Most of the similar looking plants from Africa are euphorbias. There are some similarities but the the main differences are in the structure of the spines. If you look closely at the base of the spines, you will see that euphorbia do not have areoles or the raised spots with glochids or tiny spines.