Did you know that some cactuses are actually two cactuses stuck together? In a method known as "grafting," you can take one cactus and stick it on another, and the two cactuses will live together as one entity.
You'll usually see grafted cactuses where the top is a vibrant color of yellow, orange, or red, and it sits on the stump of a green cactus. The brightly colored top cactus needs a grafted partner because it doesn't have any green in it for photosynthesis. By combining itself with the green cactus stump, the colorful grafted cactus on top can thrive.
Sometimes, grafted cactuses only live a few years before they get tired of one another. If one cactus grows faster than the other, they can become mismatched and one of them might get too stressed out and die.
The Euphorbia Lactea Cristata you see below is a grafted cactus where the top that looks like a piece of coral sits on the stump of an entirely different cactus. This particular cactus is on my front porch, and he enjoys life under the California sun.
(although, as I write this, there's a hurricane passing through Los Angeles, so I've moved him and his friends to shelter for the duration of the rain!)