Cactus vs. Succulent: What Is the Difference?

If you have ever stood in a garden center trying to figure out whether a plant is a cactus or just a succulent, you are not alone. The terms get used interchangeably all the time, which makes sense in casual conversation but misses an important distinction. Here is the actual difference.

What Is a Succulent?

A succulent is any plant that stores water in its fleshy tissues as an adaptation to dry environments. This is a broad, descriptive category, not a precise botanical one. The word comes from the Latin succulentus, meaning full of juice. Succulents are found across dozens of unrelated plant families and on every continent except Antarctica.

Common succulents include aloe (family Asphodelaceae), echeveria (family Crassulaceae), agave (family Asparagaceae), and haworthia (family Asphodelaceae). These plants have no close botanical relationship to each other. They just share the same strategy for surviving drought.

What Is a Cactus?

A cactus is a member of the family Cactaceae. All cacti are succulents by the broad definition, but they belong to a specific plant family native almost entirely to the Americas. There are roughly 1,750 known cactus species, ranging from tiny button-sized plants to towering saguaros.

The defining feature that sets cacti apart from all other succulents is the areole. Areoles are small, cushion-like structures unique to cacti, from which spines, flowers, branches, and new growth all emerge. If a plant has areoles, it is a cactus. If it does not, it is not.

The Spine Question

It is tempting to say that cacti have spines and other succulents do not, but this is not reliable. Some cacti have no spines at all, like the spineless bishop's cap (Astrophytum myriostigma). And some non-cactus succulents, like certain euphorbias, have sharp thorns that look very much like cactus spines. The difference is that euphorbia thorns grow directly from the stem tissue, while cactus spines always emerge from areoles.

Commonly Confused Plants

Euphorbia

Many euphorbias look strikingly like cacti: columnar, spiny, adapted to dry conditions. The easy way to tell them apart is to nick the skin slightly. Cacti produce a clear or watery sap. Euphorbias produce a thick white milky latex that can irritate skin and eyes. Never mistake this fluid for water. Euphorbia latex is toxic.

Agave

Agaves are sometimes mistaken for cacti because of their spiny leaf tips and desert associations, but they are monocots and not related to the cactus family.

Aloe

Aloe looks superficially similar to some smaller cacti but is in an entirely different plant family. Its toothed leaf margins are not spines from areoles. They are part of the leaf itself.