Epithelantha unguispina
| Light | Bright light with a little shade from the harshest afternoon sun |
|---|---|
| Water | Sparingly; let the mix dry out completely between waterings, keep dry in winter |
| Soil | Gritty, fast-draining mineral mix (see Soil and potting mix) |
| Temperature | Keep above freezing; roughly USDA zones 9–11 |
| Propagation | Seed; occasionally offsets on clustering plants |
| Toxicity | Non-toxic to cats and dogs |
Epithelantha unguispina is a small, globular "button cactus" from northern Mexico, closely allied to the more familiar Epithelantha micromeris. It is distinguished by its dark, projecting, claw-like central spine, which breaks the otherwise smooth, chalk-white surface of the plant — a feature that gives the species its name (from the Latin unguis, a claw or nail). Some botanists treat it as a subspecies of E. micromeris rather than a species in its own right.
Description
Epithelantha unguispina forms a small, rounded to shortly cylindrical body, solitary when young but often clustering with age, and rarely more than a few centimetres across. Like the rest of the genus it is densely covered in tiny tubercles, each tipped with a cluster of very short, white radial spines pressed flat against the body. Overlapping so tightly, these spines hide the green skin almost completely and give the plant its characteristic smooth, white, pebble-like appearance.
What sets this species apart is the central spine. Where E. micromeris has soft, deciduous central spines that often break away, E. unguispina carries a stouter, dark-tipped central spine — usually just one per areole — that curves outward and downward like a little claw or hook, standing out sharply against the pale surface. Small pink flowers, pale to deep pink and larger than in related forms, appear near the crown, followed by the elongated red fruits typical of the genus.
Distribution and habitat
The species grows in the arid limestone country of northern Mexico, chiefly around Monterrey in Nuevo León and south into San Luis Potosí, on limestone hills and rocky slopes. Plants typically wedge into cracks and gritty pockets among the rock, often growing alongside other dwarf cacti and drought-tolerant shrubs that offer a little shade. The mineral, sharply drained substrate of these habitats is a useful guide to how the plant should be potted in cultivation.
Like all cacti, the genus is listed under CITES Appendix II, so international trade is regulated; nursery-grown, seed-raised plants are the responsible choice, and wild collecting should never be considered.
Cultivation
Epithelantha unguispina is grown much as its relatives are, and the main risk is the same: overwatering. Give it a very free-draining, mostly mineral mix in a small pot, and site it in bright light with just a little protection from the fiercest afternoon sun — good light keeps the body compact and the white spination dense. Water thoroughly only once the mix has dried right through, then hold off; keep the plant dry and cool over winter, which both prevents rot and encourages flowering.
This is a slow-growing, undemanding little cactus once its watering is understood. See Watering and Repotting for general technique.
Propagation
Seed is the usual method. The fine seed germinates readily on a warm, gritty surface kept lightly humid, though seedlings are small and slow and benefit from careful, patient care in their first year or two. Plants that cluster with age can occasionally be divided, and rooted offsets provide a simple vegetative route where they are produced. See Propagation — seed and Propagation — offsets for details.
Common problems
- Rot — nearly always from overwatering or a mix that holds too much moisture; the plant softens and discolours from the base.
- Etiolation — too little light makes the body elongate and lose its neat button shape, and the spination opens up.
- Pests — red spider mites and mealybugs can hide among the dense spines and in the woolly crown; inspect regularly (see Pests and diseases).
See also
- Epithelantha — the genus overview
- Soil and potting mix · Watering · Propagation — seed · Propagation — offsets · Repotting