Tephrocactus molinensis
| Light | Full sun to very bright light |
|---|---|
| Water | Very sparingly in growth; keep bone-dry through a cold winter rest |
| Soil | Extremely gritty, fast-draining mineral mix (see Soil and potting mix) |
| Temperature | Tolerates cold if dry; protect from hard freezes and winter wet |
| Propagation | Detached stem segments (offsets); seed |
| Toxicity | Not considered toxic, but the areoles bear irritating, easily detached glochids (barbed bristles) |
Tephrocactus molinensis is a small, low-growing clumping cactus from the Salta region of northwestern Argentina. It builds up loose mounds of easily detached, rounded (globular to egg-shaped) segments — glaucous and blue- to grey-green — that are dotted with rings of prominent glochids rather than long spines, giving it the neat jointed look typical of the genus Tephrocactus. Like its relatives it is a high-altitude Andean opuntioid, prized by collectors for its compact habit and colourful, glochid-studded segments.
Description
Tephrocactus molinensis is a segmented (jointed) cactus that forms low, spreading clumps rather than a single stem. Each joint is a firm, rounded to shortly egg-shaped segment a few centimetres long, blue- to grey-green and glaucous (with a slightly waxy bloom), and the whole plant grows by adding new segments at the tips and shoulders of the old ones. The joints are only loosely attached and separate readily — a natural means of vegetative spread that is very useful in cultivation.
The segments carry few or no true spines; the plant's most conspicuous feature is instead its areoles, which bear dense glochids: fine, barbed bristles — often yellowish to orange-red — that detach at the lightest touch and lodge painfully in skin, so the plant is best handled with thick gloves or folded paper. Flowers, when they appear, are small to medium, pale (whitish to soft pink) with a green centre, and open at the joint tips in the warmer months.
Distribution and habitat
The species occurs in the Argentine province of Salta, in the arid, high-altitude valleys and slopes of the eastern Andes. Plants of this group grow in gritty, stony ground under strong sun, with cold nights, a pronounced dry season and only seasonal rainfall — conditions that favour the compact, tidy habit seen in cultivated specimens.
Cultivation
Tephrocactus molinensis is grown much as other high-Andean Tephrocactus: give it the brightest position you can, an extremely free-draining, mostly mineral mix, and restraint with the watering can. Water lightly only when the plant is in active growth and the mix has dried completely, then let it dry again.
The critical point is winter: like most of the genus it wants a cold, completely dry rest. Damp cold is the surest way to rot it, whereas dry cold is tolerated well and often improves the following season's growth. In humid climates it is safest grown under cover so that winter rain never touches the roots. See Watering and Repotting for general technique.
Propagation
Propagation is easy and usually vegetative. Because the segments detach so readily, a single joint laid on dry, gritty mix will callus and root within a few weeks in warm weather — see Propagation — offsets and Propagation — cuttings. Allow the cut or broken surface to dry for a few days before setting the segment on (not buried in) the mix, and keep it barely moist until roots take hold. The species can also be raised from seed, though germination in this genus can be slow and erratic.
Common problems
- Rot — nearly always from winter wet or a mix that holds moisture; keep the plant dry and cold in its rest period.
- Glochids — not a plant health issue but a handling hazard; the barbed bristles are difficult to remove from skin, so always handle with protection.
- Etiolation — too little light stretches the segments and spoils the compact, tidy habit.
- Pests — mealybugs (white fluff in the areoles) and root mealybugs are the usual offenders; see Pests and diseases.
See also
- Tephrocactus — the genus overview
- Propagation — offsets · Propagation — cuttings · Soil and potting mix · Watering