Mammillaria theresae
| Light | Bright light with some protection from harsh midday sun |
|---|---|
| Water | Very sparingly in growth; keep completely dry and cool in winter |
| Soil | Extremely free-draining mineral mix, deeper pot for the taproot (see Soil and potting mix) |
| Temperature | Keep above freezing; roughly USDA zones 9b–11 |
| Propagation | Seed (primary); occasionally offsets |
| Toxicity | Non-toxic to cats and dogs |
Mammillaria theresae is a tiny, tuberous-rooted miniature cactus from Durango, Mexico, prized by collectors for its feathery spines and comparatively enormous, glowing violet-pink flowers. Rarely more than a couple of centimetres across, it is one of the smaller and more sought-after members of the genus Mammillaria, and a plant that rewards careful, restrained cultivation.
Description
Mammillaria theresae forms a small, soft, cylindrical to club-shaped body, usually solitary at first but slowly clustering with age. The whole plant is diminutive — often only 1–3 cm wide — and sits atop a thick, fleshy taproot that is considerably larger than the visible stem, an adaptation to its harsh native habitat.
The tubercles are soft and closely set, each tipped with tiny, feather-like (plumose) radial spines that lie flat against the body, giving the plant a soft, downy texture rather than a spiny one. There are no fierce central spines. In spring the plant produces flowers that seem almost too big for it: broad, funnel-shaped blooms in a vivid violet to magenta-pink, often nearly as wide as the body itself, emerging low down among the tubercles.
Distribution and habitat
The species is native to a limited area of the Mexican state of Durango, where it grows in high, cool grassland and open, gravelly ground. During the dry season the small body contracts down into the soil, pulled below the surface by its taproot, so that little more than the flat top remains visible among stones and grass — a survival strategy against drought, cold and grazing.
Because of its restricted range and desirability, wild populations are vulnerable to illegal collection. Like the whole cactus family it is listed under CITES Appendix II. Nursery-grown, seed-raised plants are readily and legally available; wild collecting is not.
Cultivation
Mammillaria theresae is a choice plant that demands care with water above all. Grow it in an extremely free-draining, mostly mineral mix, and choose a pot deep enough to accommodate the substantial taproot. Give it bright light with a little shade from the fiercest afternoon sun.
Water sparingly during the growing season, always allowing the soil to dry completely between waterings, and keep the plant bone dry and cool through winter. This cold, dry winter rest is important both for flowering and for preventing rot, which — as with most tuberous-rooted miniatures — is the commonest cause of loss. The taproot is prone to rotting if kept wet, so err firmly on the side of underwatering. See Watering and Repotting for general technique.
Propagation
Seed is the usual method, and seed-raised plants are the backbone of the hobby for this species. The fine seed germinates on a warm, moist mineral surface and seedlings are grown on slowly. Mature clustering plants can occasionally be divided or their offsets removed and rooted, though this species offsets less freely than many mammillarias. See Propagation — seed and Propagation — offsets for details.
Common problems
- Rot — by far the biggest risk, almost always from overwatering, a slow-draining mix, or a cold, wet winter; the fleshy taproot and body soften and discolour.
- Etiolation — too little light makes the small body stretch and lose its compact form.
- Pests — mealybugs (white fluff among the tubercles, and on the roots) and red spider mites are the usual offenders; root mealybugs are especially worth checking for at repotting.
See also
- Mammillaria — the genus overview
- Soil and potting mix · Watering · Repotting · Propagation — seed · Propagation — offsets · Pests and diseases