Thelocactus
Thelocactus is a small genus of about a dozen species of globular to short-cylindrical cacti native to Mexico and adjacent southern Texas. The name (from the Greek thele, "nipple") refers to the pronounced tubercles or knobby ribs that give many species a bumpy, warted outline. What really wins them their following, though, are the flowers: large, funnel-shaped and often strikingly multicoloured, they crown the plant in spring and early summer and are big in proportion to the modest bodies that produce them.
Description
Thelocacti are typically solitary (occasionally clustering with age), forming a firm green to blue-green body that is somewhere between a flattened globe and a short column. The ribs are usually broken up into distinct tubercles — the "nipples" of the name — each tipped with an areole bearing stout, sometimes flattened or papery, spines. Spination varies enormously across the genus, from sparse and comb-like to dense and showy, and can be a major part of a plant's appeal.
The flowers are the highlight: broad, funnel-shaped and often quite large relative to the plant, in shades of magenta, pink, yellow and white, frequently with a contrasting darker throat. They open near the growing tip over several days. Fruits are small, dryish capsules that split to release the seed.
Distribution
The genus is centred on the arid and semi-arid regions of central and northern Mexico, with a couple of species reaching into the Chihuahuan Desert of southern Texas. Plants grow on limestone hills, gravelly flats and rocky slopes, often wedged among rocks in thin, sharply drained soils and exposed to strong sun.
Notable species
- Thelocactus bicolor — the "glory of Texas", perhaps the best-known species, valued for its colourful spines and large magenta-pink flowers that usually have a contrasting red throat.
- Thelocactus setispinus — the "miniature barrel" or fishhook-bristle cactus, an easy, free-flowering beginner's plant with hooked spines and yellow blooms with a red throat. (It is sometimes placed in Ferocactus or Hamatocactus, depending on the classification followed.)
- Thelocactus hexaedrophorus — a low, strongly tubercled species with a flattened, geometric outline and pale pink to white flowers.
- Thelocactus rinconensis — a broad, blue-grey plant with very prominent tubercles and reduced spination.
- Thelocactus tulensis — a variable, clustering species from around Tula.
Species boundaries within Thelocactus are debated, and several names have been moved in and out of the genus over the years, so plant labels do not always agree.
Cultivation
As a group, Thelocacti are among the more forgiving of the "collector" cacti, though the usual mineral-cactus rules apply. Grow them in a very free-draining, mostly mineral mix in a snug pot, and give them the brightest light you can manage — good light brings out the best spine colour and encourages flowering. Water thoroughly through the growing season once the soil has dried, then ease right off in autumn; keep them dry and cool over winter, which both prevents rot and sets up the following season's flowers. See Watering and Repotting for general technique.
Most species tolerate a cold, dry winter rest well and can take a light touch of frost if bone dry, but for safety keep them above freezing. Overwatering and a soggy mix are, as ever, the commonest causes of loss.
Hobby and cultivar notes
Thelocactus is grown mainly for the wild-type species rather than for named cultivars, and part of the appeal is the natural variation in spine form and flower colour from plant to plant. T. setispinus in particular is a popular, cheap and quick-flowering starter cactus, while T. bicolor is prized for its spines. The genus also crosses readily in cultivation, and intergeneric hybrids with related groups turn up occasionally.
See also
- Thelocactus bicolor · Thelocactus setispinus — popular species
- Soil and potting mix · Watering · Repotting · Propagation — seed
- Pests and diseases