Epithelantha pachyrhiza
| Light | Bright light with some protection from the fiercest afternoon sun |
|---|---|
| Water | Sparingly; allow to dry fully between waterings, dry rest in winter |
| Soil | Very gritty, fast-draining mineral mix (see Soil and potting mix) |
| Temperature | Keep above freezing; roughly USDA zones 9b–11 |
| Propagation | Seed (primary); offsets where clustering forms occur |
| Toxicity | Non-toxic to cats and dogs |
Epithelantha pachyrhiza is a small, pale-spined button cactus endemic to a small area near Saltillo, in the state of Coahuila in northeastern Mexico. Its most distinctive feature sits out of sight: a stout, tuberous taproot that swells well beyond the size of the modest above-ground body, an adaptation for storing water and surviving the long dry spells of its limestone habitat. The species name pachyrhiza — literally "thick root" — refers directly to this trait, and many authors treat the plant as a subspecies of the widespread Epithelantha micromeris.
Description
Epithelantha pachyrhiza forms a small body that is rounded when young but tends to elongate with age, becoming top-shaped to shortly columnar and reaching roughly 10 cm tall in older plants. Like the rest of the genus, the body is set with tiny, pale spines — white to orange- or bluish-tan — pressed close to the skin and radiating from crowded areoles at the tips of very small tubercles. In this species the spines are comparatively few and short, so they only partly cover the stem and the green body is not entirely concealed.
The defining feature is below ground: a thick, tuberous to carrot-like taproot that can be considerably larger than the visible stem. This swollen root anchors the plant and stores moisture, allowing it to shrink back into the ground and wait out drought. Small flowers appear at the crown, pinkish-white and inconspicuous — they barely emerge above the woolly apex — and are followed by the slender red fruits characteristic of Epithelantha.
Distribution and habitat
The species is a narrow endemic of northeastern Mexico, restricted to a small area around Saltillo in the state of Coahuila. It grows on rocky, calcareous (limestone) ground in arid scrub, usually rooted into crevices and gritty pockets where drainage is sharp and organic matter scarce. In such settings the tuberous root is a clear advantage, letting the plant draw on stored water during extended dry periods while the compact body minimises exposure.
Like all cacti, the genus is listed under CITES Appendix II, so international trade in wild-collected plants is regulated. Nursery-grown, seed-raised specimens are the responsible source for collectors; wild collection is discouraged and, in many areas, illegal.
Cultivation
Epithelantha pachyrhiza is a slow, undemanding plant for the collector who can resist the watering can. Because of its large water-storing root, it is especially sensitive to staying wet, and rot is the most common cause of loss. Grow it in a very gritty, mostly mineral mix in a pot deep enough to accommodate the tuberous root, and water thoroughly only once the soil has dried out completely. Keep the plant dry and cool through winter, which both prevents rot and encourages flowering.
Give it bright light with a little shade from the most intense afternoon sun to keep the spination dense and the body compact. See Watering and Repotting for general technique; when repotting, handle the swollen root carefully and let any damage callus before watering again.
Propagation
Seed is the standard and most reliable method. The fine seed germinates on a warm, gritty surface kept lightly humid, though seedlings are slow and benefit from careful, patient culture in their first years. See Propagation — seed for a full walkthrough. Where plants cluster or offset, those offsets can be removed and rooted, but seed remains the primary way of raising this species. Some growers speed up seedlings by grafting, later growing them on their own roots. See also Propagation — offsets.
Common problems
- Rot — by far the biggest risk; almost always from overwatering, a slow-draining mix, or water sitting around the tuberous root. The plant softens and discolours from the base.
- Etiolation — too little light makes the body swell and lose its tight form and dense spination.
- Pests — red spider mites and mealybugs (white fluff nestled among the areoles) are the usual offenders; see Pests and diseases.
See also
- Epithelantha — the genus overview
- Epithelantha micromeris — the closely related, widespread relative
- Grafting · Soil and potting mix · Watering · Propagation — seed · Propagation — offsets