Thelocactus tulensis
| Light | Bright light to full sun |
|---|---|
| Water | Sparingly in the growing season; 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; plants are usually solitary |
| Toxicity | Not known to be toxic to cats or dogs |
Thelocactus tulensis is a small to medium-sized, usually solitary cactus from the limestone hills of northeastern Mexico, prized by Thelocactus specialists for its prominent, conical tubercles and its delicate whitish to pale-pink flowers. It is a variable, polymorphic species linking numerous intergrading geographical forms, and remains a manageable, collectible plant well suited to a mixed cactus collection.
Description
Thelocactus tulensis produces globose to shortly cylindrical stems, reaching around 25 cm tall and 8 cm across, that are a dull dark green and typically solitary. The body carries about ten ribs broken up into prominent, conical tubercles, each often with a chin-like projection beneath the areole — a feature that gives the plant its characteristic geometric look.
Spines are borne from woolly areoles at the tubercle tips: shorter pale radials that whiten with age, together with a few longer, straight or curved centrals that are whitish to horn-coloured with a darker tip. The flowers open by day near the crown and are usually silvery-white to soft pink, each tepal marked with a darker carmine midstripe, appearing in the warmer months.
Distribution and habitat
The species is native to the Chihuahuan Desert of northeastern Mexico — in the states of Tamaulipas, Nuevo León and San Luis Potosí — where it grows on limestone hills and rocky, gravelly slopes among low shrubs and grasses, generally at elevations of about 1200–1900 m. As with many members of the genus, plants root in gritty, well-drained ground and are exposed to strong sun and pronounced seasonal drought.
Like all cacti, Thelocactus tulensis is listed under CITES Appendix II, which regulates international trade. Nursery-propagated plants are the responsible and legal source for collectors; wild collection is discouraged and, in many cases, unlawful.
Cultivation
Thelocactus tulensis is a straightforward grower by the standards of the genus, provided its roots are never left wet for long. Plant it in a very free-draining, mostly mineral mix and give it bright light to full sun to keep the body compact and the spination strong. Water thoroughly during the growing season once the soil has dried out, then reduce watering sharply as autumn arrives.
Keep the plant cool and completely dry through winter, which both prevents rot and helps promote flowering the following season. See Watering and Repotting for general technique. In cultivation the species is usually hardy only to just above freezing, so growers in cold climates overwinter it under glass or indoors.
Propagation
Seed is the usual and most reliable method, sown on a warm, gritty surface kept lightly humid until germination; see Propagation — seed for a full walkthrough. Because plants are typically solitary, vegetative increase is seldom possible; should a plant ever produce an offset it can be removed and rooted as an offset, but this is uncommon in this species.
Common problems
- Rot — the most common cause of loss, almost always from overwatering or a slow-draining mix; heads soften and discolour from the base.
- Etiolation — too little light makes the stem grow soft, pale and elongated, blurring the crisp tubercle shape.
- Pests — mealybugs (white fluff in the areoles and around the roots) and red spider mites (fine webbing and bronzed skin) are the usual offenders; see Pests and diseases.
See also
- Thelocactus — the genus overview
- Soil and potting mix · Watering · Propagation — seed · Propagation — offsets · Repotting