Thelocactus conothelos
| Light | Bright light to full sun |
|---|---|
| Water | Sparingly; let the mix dry fully between waterings, dry rest in winter |
| Soil | Gritty, fast-draining mineral mix (see Soil and potting mix) |
| Temperature | Keep above freezing; roughly USDA zones 9b–11 |
| Propagation | Seed (primary); occasional offsets on clustering plants |
| Toxicity | Non-toxic to cats and dogs |
Thelocactus conothelos is a globular to shortly columnar cactus from the arid highlands of northeastern Mexico, prized by collectors for its strongly tuberculate body and its remarkably variable spination and flower colour. Depending on the subspecies, the same species can bear magenta, yellow to orange, or white blooms, which — together with wide differences in spine length and density — makes it one of the more rewarding members of the genus Thelocactus to grow. It was originally described as Echinocactus conothelos.
Description
Thelocactus conothelos forms a solitary green to blue-green body, at first rounded and becoming shortly columnar with age, that is broken up into prominent conical tubercles rather than continuous ribs — the feature that gives the genus its name (from the Greek thele, "nipple"). Older plants may cluster modestly, but many remain single.
Spination is the most variable trait in the species. Areoles sit at the tips of the tubercles and may carry anything from a few short, stiff spines to a dense, spreading array of longer central and radial spines; colour ranges through white, grey, yellowish and brown. Flowers open from near the crown in spring and summer, funnel-shaped and comparatively large for the plant, in shades that track the subspecies — magenta to purple, yellow to orange, or white. This flexibility of colour is a large part of the species' appeal to collectors.
Distribution and habitat
The species is native to northeastern Mexico, chiefly in the states of Nuevo León, San Luis Potosí and Tamaulipas. It grows in dry scrub, grassland and rocky limestone slopes at moderate elevation, often tucked among rocks and low vegetation that give it a little seasonal shade and sharp drainage. Several subspecies have been described from these populations, differing in spination and flower colour, and much of the confusion in older names reflects this natural variation across its range.
Cultivation
Thelocactus conothelos is a straightforward grower by cactus standards, provided it is kept lean and dry. Use a very free-draining, mostly mineral mix and a pot that is snug rather than oversized, and give it bright light to full sun to encourage strong spination and flowering. Water thoroughly only once the soil has dried out completely through the growing season, then let it dry again; keep the plant dry and cool over winter to prevent rot and to help set flower buds. As with most desert cacti, overwatering — especially in a heavy mix — is the main cause of loss. See Watering and Repotting for general technique.
Propagation
Seed is the usual and most reliable method. The seed germinates well on a warm, gritty surface kept humid until the seedlings establish, and growing from seed is also the best way to appreciate the species' natural variation in spine and flower colour. Plants that cluster can occasionally be increased by removing rooted offsets, though this is far less common than seed. See Propagation — seed and Propagation — offsets for full walkthroughs.
Common problems
- Rot — nearly always from overwatering or a slow-draining mix; the body softens and discolours from the base.
- Etiolation — too little light makes the plant grow pale, soft and elongated, with weaker spination.
- Pests — red spider mites and mealybugs are the usual offenders; watch for fine webbing and white fluff in the tubercle axils. See Pests and diseases.
See also
- Thelocactus — the genus overview
- Soil and potting mix · Watering · Repotting · Propagation — seed · Propagation — offsets