While the African milk tree looks like a cactus, it is not actually a cactus, but rather a succulent (or euphorbia). While all cacti are succulents, not all succulents are cacti. A cactus is a very specific group of succulents that are identified as having an areole, which is a small nodule that contains small hairs and/or needles. The African milk plants do not have these areoles, therefore is not a cactus.