Update May 2022:  It’s a goner. It is easy to grow, but hard to keep growing, due to our very wet summers.   I could see the bottom turning brown, and very slowly moving up.

If you live in Arizona, Nevada or southern California, this is a pretty ordinary cactus.  In Miami, it isn’t common.   I’ve tried hard to provide ample drainage, so when our very wet summer hits, the cactus might survive.  Planting on top of a hill would be good, except Miami is as flat as a pancake.   Still, I’ve seen them grow on top of a large coral rock.

I believe it is also called mother in law’s cushion in Spanish.