Is It a Cactus?
Cactus identification comes down to one feature almost everyone overlooks: the areole. A cactus is a plant in the family Cactaceae, and every cactus, spiny or smooth, carries these small felted cushions that spines, hairs and flowers grow from. Nothing else in the plant world has them. At rarecactus.com we grow every plant from seed and match it to its wild field-number record, so telling a true cactus from a look-alike is the first skill we lean on. Use the quick tool below, then read how the test works.
Not sure if it is a cactus?
Answer a few quick questions about what the plant looks like. The tool checks for the one feature only cacti have, then tells you what you are actually looking at and why.
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How to tell a cactus from a succulent
All cacti are succulents, but not all succulents are cacti. A succulent is any plant that stores water in fleshy stems or leaves; a cactus is the subset of succulents in the family Cactaceae, defined by the areole. Many plants sold as cacti are actually euphorbias, agaves or living stones. The table below is the fast way to place a plant, and the areole row is the one that settles it.
| Feature | Cactus | Euphorbia | Agave & aloe | Other succulents |
|---|---|---|---|---|
| Areoles (spine cushions) | Yes, the defining feature | No | No | No |
| Where spines come from | Clusters from the areole | Thorns from the stem, often paired | Teeth on leaf edges, spine at the tip | Usually none |
| Sap when cut | Clear and watery | Milky white latex, an irritant | Clear | Clear |
| Leaves | Usually none | Often none, sometimes small and quick to drop | Thick leaves in a rosette | Fleshy leaves |
| Flowers | Many petals and stamens, from an areole | Tiny, in a cup-like cyathium | Tall flower spike | Varied |
| Native range | The Americas, one exception | Africa, Madagascar and beyond | Americas and Africa | Worldwide |
What is an areole?
An areole is a small, cushion-like bump on a cactus stem, often felted or woolly, that spines, hairs, branches and flowers all grow from. It is the single feature that defines the cactus family. If a spiny plant has no areoles, it is not a cactus, no matter how much it looks like one. This is why a spiny euphorbia is not a cactus: its thorns rise straight from the stem, with no cushion at the base. A hand lens helps, but on most cacti the areoles are easy to see once you know to look for the felted pad rather than the spine itself.
Cactus or euphorbia?
Euphorbias are the look-alikes that fool people most, because many are spiny, ribbed and column-shaped just like a cactus. Two tests separate them. First, the sap: nick a small spot and a euphorbia bleeds a milky white latex, while a cactus runs clear. That latex is an irritant, so keep it off skin and eyes. Second, the areole: a cactus grows its spines from felted cushions, a euphorbia grows paired thorns straight from the stem. If you want the full walk-through, see the 60-second areole test. For the plants themselves, browse the rare cactus encyclopedia or the harder cases like the living rock cactus, which hides flat in the gravel and still shows textbook areoles once you find them.
Frequently Asked Questions
Is it a cactus or a succulent?
It is likely both. All cacti are succulents, but not all succulents are cacti. A cactus is a succulent in the family Cactaceae, set apart by areoles, the felted cushions its spines and flowers grow from. If the plant stores water but has no areoles, it is a succulent that is not a cactus.
How can you tell if a plant is a cactus?
Look for areoles: small round cushioned pads on the stem that spines, hairs and flowers emerge from. Only cacti have them. Check the sap too, since a cactus runs clear while a euphorbia bleeds milky latex. Areoles plus clear sap means a cactus.
What is an areole?
An areole is the small, often woolly cushion on a cactus body from which spines, branches and flowers grow. It is the one feature unique to the cactus family, Cactaceae, and the reliable test for whether a plant is a true cactus.
Is it a cactus or a euphorbia?
Cut a small spot on the stem. A euphorbia leaks milky white latex, a cactus does not. A cactus also grows spines from areoles, while a euphorbia grows paired thorns straight from the stem. The milky sap is the quickest tell, so wash your hands after.
Do all cacti have spines?
No. Some cacti, such as Lophophora and the smooth Astrophytum asterias, have few spines or none at all. They are still cacti because they keep their areoles, which show as small woolly dots arranged in a pattern across the body.
The 60-second areole test · Rare cactus encyclopedia · Rare cactus types · Living rock cactus · Anderson, E.F., The Cactus Family (Timber Press) · Royal Botanic Gardens Kew, Plants of the World Online (POWO) · Nyffeler & Eggli, Cactaceae phylogeny