Tephrocactus alexanderi
| Light | Bright light to full sun; a little shade from the fiercest afternoon sun |
|---|---|
| Water | Sparingly; allow to dry fully between waterings, keep dry through winter |
| Soil | Very gritty, fast-draining mineral mix (see Soil and potting mix) |
| Temperature | Keep above freezing; hardy to light frost when bone dry (roughly USDA zones 9–11) |
| Propagation | Segments (joints) and seed |
| Toxicity | Not known to be toxic to cats or dogs, but the glochids cause mechanical injury |
Tephrocactus alexanderi is a small, clump-forming cactus from arid western Argentina, built from a chain of loosely attached, rounded to egg-shaped segments. Each joint carries a scattering of pale, curved spines, and the plant produces relatively large white to soft-pink flowers that seem oversized for its modest body. It is one of the more widely grown members of the genus Tephrocactus among collectors of miniature opuntioid cacti.
Description
Tephrocactus alexanderi grows as a low, branching cluster of detachable segments, each joint typically globular to shortly egg-shaped and only a few centimetres long. The segments are greyish to bluish green, sometimes flushed with purple in strong light, and their skin is firm and slightly tuberculate. Where one joint meets the next the connection is narrow and brittle, so segments break away easily — a habit that doubles as the plant's main means of vegetative spread.
The areoles bear short white wool and tufts of fine, irritating glochids, along with a few spines. These spines are sparse, pale, and characteristically straight to slightly curved, a few of them thin and pressed close to the segment. Flowers open at the tops of the segments in the warmer months: comparatively large and showy for the size of the plant, in shades of white through to pale pink, and followed by dryish fruit.
Distribution and habitat
The species is native to the dry interior of western Argentina, where it grows on open, stony flats and gentle slopes among sparse desert scrub. These are continental habitats with strong sun, big swings between day and night temperatures, a short summer rain season, and long dry spells the rest of the year. Plants sit in gritty, sharply drained ground and are adapted to going bone dry for extended periods.
Cultivation
Tephrocactus alexanderi is not difficult if its need for sharp drainage and a hard dry rest is respected — the usual cause of loss is overwatering, especially in cool weather. Grow it in a very gritty, mostly mineral mix in a pot that drains freely, and give it as much bright light as you can; strong light keeps the segments compact and encourages the curved spines and any purple tinting. See Watering for general technique.
Water thoroughly during the warm growing season once the soil has dried out, then let it dry completely again before the next drink. Through winter keep the plant dry and cool to prevent rot and to encourage flowering; kept dry it will shrug off light frost, though prolonged cold damp is fatal. When handling the plant, beware the glochids, which lodge in skin at the slightest touch — see Repotting for tips on moving spiny, brittle-jointed cacti safely.
Propagation
Because the segments detach so readily, the easiest method is simply to remove a joint, let the broken surface callus for several days, and set it on top of a gritty mix until it roots. This is essentially the offset and cutting approach rolled into one, and it reliably produces plants identical to the parent. Seed is also possible for those wanting variation or larger numbers, though germination in opuntioid cacti can be slow and erratic; see Propagation — seed.
Common problems
- Rot — the leading killer, almost always from too much water, a mix that holds moisture, or watering while cold. Segments go soft and discoloured.
- Etiolation — too little light makes joints elongate and lose their tight, rounded form and colour.
- Glochids — not a plant problem but a grower one; the fine barbed bristles detach at a touch and are a nuisance to remove from skin. Handle with folded paper, tongs, or thick gloves.
- Pests — mealybugs (white fluff in the areoles, and on the roots) and occasionally red spider mites.
See also
- Tephrocactus — the genus overview
- Soil and potting mix · Watering · Propagation — offsets · Propagation — cuttings · Propagation — seed · Repotting · Pests and diseases