human
I'd like to know more about the different types of cacti.
assistant
There are over 2,000 species of cactus in the world. They are divided into two main groups, those that have spines and those that do not. The ones with spines tend to be taller and more robust than their spineless cousins. The most common type is the prickly pear (Opuntia), which has a flat pad on its stem that can easily be broken off. This type of cactus is often seen as a hedge or fence.