If you grow cactus and other succulents, you probably have a few euphorbias mixed in with the cacti. Source: mashtalegypt.com, montage: laidbackgardener.blog
In the world of succulents, that is, plants that store water in thickened stems or leaves in order to better cope with arid conditions, two different families are often mistaken one for the other: cacti (Cactaceae) and euphorbias (Euphorbiaceae, genus Euphorbia). In fact, many people simply call all succulent euphorbias “cacti,” not realizing there is a difference.
Both cacti and euphorbias tend to be stem succulents, that is, they store moisture in swollen stems, both tend to very spiny and both include a variety of species of all different shapes. They are so similar in many aspects that confusion is understandable, yet they are no more closely related to each other than dogs are to cats.
Dogs and cats are both mammals, are covered in hair, have tails and pointy teeth and are carnivores, yet few people would confuse a dog with a cat. If you’re a gardener, you really should learn to tell a euphorbia from a cactus. Once you know the difference, you’ll never confuse them again.
The similar appearance of cacti to euphorbias is an example of convergent evolution: the two different families evolved under similar conditions—under extreme aridity—and adopted similar survival tactics, resulting a lot of similarities. Even so, they also have their differences.
Telling the Two Apart
Here are a few tips on telling the euphorbias from cacti. You may well find you’re growing both of them without knowing it!
- Cacti have areoles. These are cushiony, fuzzy dots from which spines, stems and flowers grow. They can be white or yellow, but are present on all cacti. No other plant has areoles. So, if you look closely at any cactus-like plant and see no areoles, as will be the case with euphorbias, that plant is definitely not a cactus! This is, hands down, the easiest way of telling the two apart. Once you know this, you’ll never confuse a cactus with any other plant again!
*Be aware that unscrupulous cactus growers often stick fake flowers on cactus with glue guns. If the flower on a cactus does not grow from an areole and has a glob of glue underneath, you’ve been had!
- Cacti are almost always leafless, at least as adults (all bear two cotyledons at germination). There are only a few exceptions (Pereskia, which actually don’t look like cactus at all, and a few Opuntia, for example). On the other hand, many euphorbias with succulent stems nevertheless bear leaves.
- Cacti evolved in the New World and are found in North, South and Central America as well as in the Caribbean. (There is only one species, Rhipsalis baccifera, that is native to the Old World.) Succulent euphorbias evolved in the Old World, mostly Africa, Madagascar and drier areas of Asia. In the wild, both are still mostly found in their native lands, although some cacti, notably in the genus Opuntia, have escaped from culture to become weeds in other parts of the world.
There you go! It isn’t all that hard to tell euphorbias from cacti. Just the lack of an areole on euphorbias should be such an obvious difference that you’ll never confuse the two again!