Every cactus is a succulent, and most succulents are not cacti. That one sentence settles the cactus vs succulent question, and you can stop guessing in the garden center. Succulent describes what a plant does, which is store water in fat stems, leaves or roots, and many unrelated plant families do exactly that. Cactus names a single family, Cactaceae. Every member of that family carries one feature no other plant on earth has, the areole, a cushion-like bud where spines, flowers and new branches all grow out.
"So which of these are actual cacti?" my neighbor asked me, waving at the wide south-facing windowsill in the upstairs room. Nine pots sat there. She picked out the aloe and the pencil cactus first, because the pencil cactus has the word printed right on the plastic tag. Neither one belongs to the family. Aloe is native to Africa and Arabia, and the pencil cactus is a Euphorbia wearing a borrowed name. I checked all nine pots on that sill and came up with three that carried areoles.
Water storage is a survival strategy, and separate branches of the plant world arrived at the same answer on their own. Agaves, jade plants, stonecrops, aloes and the whole Euphorbia crowd hold water in thick tissue, and none of them sit anywhere near cacti on the family tree. Cactaceae stands apart. CSU Extension puts the family at about 2,000 species, all perennial, all succulent, and all native to the Americas. So if your plant traces back to Africa or Arabia, you do not own a cactus, whatever the label says.
The areoles on cacti are easy to pick out once you know the shape. Look for a small felt-like pad on the stem, with the spines growing out of that pad in a tight cluster. Bare green skin, with spines rising straight from the surface, means you are holding something else. The family spreads from southern Canada down to the Patagonian steppe in Argentina. That one small structure holds true across the whole range, in ribbed columns, flat pads and the round ones sold in thimble pots.
Prickly pear shows the structure better than any plant you can buy. Look across a pad and you see rows of dots spread over the surface, and every dot is an areole. Each one carries glochids along with the long spines, and glochids are tiny barbed hairs that irritate skin. Never grab a pad bare-handed. The pads are modified stems with a waxy coating, and the spines are modified leaves, which is why your prickly pear looks like it has no foliage at all.
Cactus identification takes five seconds in a shop. Get your eye level with the stem and look at the base of a spine cluster for a dull, cushiony pad. Pad there, and you have a cactus. Spines coming straight out of smooth skin, or thorns running in pairs along a woody stem, and you have a succulent from some other family. Plant tags lie often enough that you should trust your own eyes first.
Tip the pot toward the light and look for the felt pad under each spine cluster. That pad is the whole cactus vs succulent split, and you can see it in one glance.
Care is the short part of this. Both groups want fast-draining soil and much less water than a leafy houseplant, so a mixed shelf gives you no trouble at all. The difference matters when you buy. Ask for a cactus and you can still walk out with a Euphorbia that grows into a shape you never planned for. Check the areole and you will know what came home with you.
Read the full article: Cacti Are Not Hard to Kill, Just Hard to Read
