A habit, not a family. Succulence is water-storage tissue, and it has appeared independently many times across the plant kingdom. The plants on a single nursery bench can come from Crassulaceae, Asphodelaceae, Aizoaceae, Asparagaceae and Cactaceae, families whose common ancestors were nothing like each other. Water can be stored in almost any organ: leaves, stems, roots, even the swollen rays of thick-trunked trees (Males, 2017). What looks like a family resemblance is convergence.

Why they can afford to sit dry. Many of these plants run crassulacean acid metabolism, or CAM, a photosynthetic pattern that opens the leaf pores at night to take in carbon dioxide, banks it as an acid until morning, and keeps the pores shut through the heat of the day. Doing the gas exchange at night, when the air is cool and damp, wastes far less water than doing it at noon. CAM is documented in 370 genera across 38 families, with a minimum of 66 separate origins (Gilman et al., 2023). Worth knowing: CAM is not a desert badge. Plenty of CAM plants are tropical forest epiphytes, which is why one member of the roster below wants nothing to do with the dry regime.

Light. Light is usually the limiting factor indoors. Most of this group wants six to eight hours of bright indirect light and does better with ten or more; arid cacti are the exception and want a south or west window with several hours of direct sun (Steil, 2024; Clemson Cooperative Extension, 2015). Starved of light they etiolate, which is the word for the stretch that comes with hunting for it: stems lengthen, the spacing between leaves opens up, new growth comes in pale, and rosette formers flatten and splay as they reach. On many barrel cacti that stretched growth is permanent and stays with the plant even after the light improves. Moving a plant abruptly from a dim corner into full sun burns it, and the scorched tissue never recovers, so make the change slowly (Steil, 2023).

Water. Soak and dry, and ignore the calendar. Water until it runs from the drainage hole, empty the saucer, then wait until the mix is dry several inches down before you water again. How long that takes depends on light, pot, mix and season, so check rather than schedule; a wooden skewer pushed into the mix comes out darkened if there's still moisture down there. They do want real water when they get it. Growth speeds up markedly on a proper wet-dry cycle compared with a plant that gets a dribble every week (Steil, 2024). In winter, desert cacti go down to just enough to keep them from shrivelling (Clemson Cooperative Extension, 2015).

Substrate and container. Aim for roughly two parts mineral to one part organic: perlite, pumice, coarse sand or fine gravel cut with potting soil, bark or coir. Straight potting soil holds too much water. The pot needs a drainage hole, and a layer of gravel in the bottom of a pot without one is not a substitute for it (Steil, 2024). Go a size up at most when repotting, because a large volume of mix around a small root system stays wet long enough to rot it (Clemson Cooperative Extension, 2015). Terracotta is porous and dries faster than plastic or glazed ceramic, which is a feature here.