Identifying Ariocarpus

Ariocarpus are built to be overlooked. They sit flat in the dirt, the color of the rocks around them, and a passing eye slides right over them. Once you know what to look for, though, the genus is easy to place, and the species sort out by just a few features.

What makes it an Ariocarpus

Five things, taken together, mark the genus:

• No spines on the adult plant. A few seedlings carry them briefly, then lose them.
• A body that sits flush with the ground or below it, growing off a thick taproot that pulls the plant down in drought.
• Triangular, leaf-like tubercles laid out in a flat rosette, not the ribs or round bumps you see on most cacti.
• A patch of wool in the center of the rosette. Flowers come straight out of that wool, usually in fall.
• Small, smooth, club-shaped fruit that often stays hidden in the wool until it dries.

Sorting out the species

Once you know it is an Ariocarpus, the tubercles do most of the work:

• A. fissuratus: broad tubercles with a hard, cracked, fissured top, like dried mud. Flush with the soil. Light magenta flowers.
• A. retusus: bigger, smoother, sharply triangular tubercles, and it sits up above the ground rather than flat in it. The largest species.
• A. trigonus: tall, narrow, incurved tubercles and yellowish flowers, unlike the magenta and pink of the rest.
• A. kotschoubeyanus: tiny and nearly buried, each narrow tubercle carrying one woolly furrow down its middle. Pink flowers.
• A. agavioides: long, narrow, agave-like tubercles that look nothing like the others in the genus.
• A. scaphirostrus: thick, keeled, boat-shaped tubercles. A local Nuevo León plant.
• A. bravoanus: small, from San Luis Potosí; subsp. hintonii is smaller still.

The two most often mixed up are fissuratus and retusus. The quick test: if the tubercle surface looks like cracked pottery and the plant sits flush with the ground, it is fissuratus. If the tubercles are smooth and the plant stands a little proud of the soil, it is retusus.

Telling them apart is one half of the job; keeping them alive is the other, covered in our Ariocarpus care guide on the companion site.