Thelocactus rinconensis
| Light | Bright light to full sun; a little shade in the fiercest summer heat |
|---|---|
| Water | Moderate in growth, allow to dry fully between waterings; keep dry in winter |
| Soil | Gritty, fast-draining mineral mix (see Soil and potting mix) |
| Temperature | Keep above freezing; roughly USDA zones 9–11 |
| Propagation | Seed (see Propagation — seed) |
| Toxicity | Non-toxic to cats and dogs |
Thelocactus rinconensis is a solitary, globular to slightly flattened cactus from the arid limestone country of northeastern Mexico. It is one of the most variable members of the genus Thelocactus, with plants ranging from broad, low-spined bodies to forms bearing long, twisted grey spines, and it produces funnel-shaped flowers — white to pale pink, or yellowish in some forms — from the crown. Because of this variability it has long absorbed a number of separately described forms as synonyms, including the well-known Thelocactus lophothele and Thelocactus nidulans.
Description
Thelocactus rinconensis forms a firm, solitary body that is depressed-globular and usually broader than tall, typically blue-green, grey-green or slightly glaucous. The body is ribbed, with the ribs broken up into large, prominent conical tubercles — a defining trait of the genus — each carrying a woolly areole at or near its tip.
Spination is the most changeable feature. Some plants (the form long called lophothele) are nearly spineless or carry only a few spines, while others (the nidulans form) bear long, flattened, often twisted grey spines that can arch over the crown. This range of appearance is entirely normal within the species and much of it depends on locality and individual plant.
Flowers open from the woolly apex in spring and summer. They are broadly funnel-shaped, white to pale pink — yellowish in the form long called lophothele — and often carry a slightly darker midstripe on the outer petals, giving a soft two-tone effect against the bluish body.
Distribution and habitat
The species is native to the Chihuahuan Desert region of northeastern Mexico, chiefly in the states of Coahuila and Nuevo León and adjacent areas. It grows on limestone hills, rocky flats and gravelly slopes, usually rooted in shallow, sharply drained mineral soils under strong sun and among sparse desert scrub.
As with the whole cactus family, Thelocactus rinconensis is listed under CITES Appendix II. Nursery-propagated plants are widely available and legal to own and trade; collecting from the wild is not.
Cultivation
Thelocactus rinconensis is an undemanding and rewarding plant for the collector, tougher than many desert cacti provided it is not overwatered. Grow it in a very free-draining, mostly mineral mix in bright light to full sun; strong light keeps the body compact and encourages the best spine development in the long-spined forms.
Water thoroughly during the warm growing season once the soil has dried, then let it dry again, and keep the plant dry and cool through winter to prevent rot and to promote flowering. It tolerates heat well and appreciates good ventilation. See Watering and Repotting for general technique.
Propagation
Seed is the usual method. The seed germinates readily on a warm, gritty surface kept lightly humid, and seedlings grow at a moderate, steady pace. Because the species is normally solitary and seldom offsets, vegetative propagation is uncommon; see Propagation — seed for a full walkthrough, and Grafting if speeding up young seedlings is desired.
Common problems
- Rot — the main cause of loss, almost always from overwatering or a slow-draining mix; the body softens and discolours from the base.
- Etiolation — too little light makes the plant elongate and pale, and long-spined forms produce weaker, sparser spines.
- Pests — mealybugs (white fluff in the areoles and around the roots) and red spider mites are the usual offenders; see Pests and diseases.
See also
- Thelocactus — the genus overview
- Soil and potting mix · Watering · Propagation — seed · Repotting · Pests and diseases