Cactus and succulent house
Is it a cactus or a succulent? Both, of course. A better question is, "Is it a Cactus or a Euphorbia?"
I painted the illustrations for the new Sybil B. Harrington Cactus and Succulent Galleries at the desert Botanical Garden in Phoenix, Arizona.
Which plant below is a Cactus and which is a Euphorbia? (Hint: read the labels.) Euphorbia plants from the dry areas of Africa look a lot like cacti, which only grow in North and South America. People often confuse them, but they are unrelated, a product of parallel evolution. The key to identifying a cactus that it has an ariole. See the illustration below for an ariole.
Congratulations, you just had a casual learning experience.