Epithelantha polycephala
| Light | Bright light to full sun; light shade in the fiercest summer heat does no harm |
|---|---|
| Water | Sparingly; allow to dry completely between waterings, keep dry in winter |
| Soil | Gritty, fast-draining mineral mix (see Soil and potting mix) |
| Temperature | Hardy to about −12 °C (USDA zones 8–11) if kept completely dry; protect from wet cold |
| Propagation | Seed; division of offsets from established clumps |
| Toxicity | No reliable pet-toxicity data; the genus contains alkaloids and has traditional use as a "false peyote," so best treated as inedible. Spines are a physical hazard. |
Epithelantha polycephala is a freely clustering "button cactus" from northern Mexico that forms low, dense clumps of many small, white-spined heads. Where most members of the genus stay solitary or offset only sparingly, this species branches abundantly, and an old plant may build up a mound of a hundred or more crowded stems — a habit reflected in its epithet, which means "many-headed." It is most often treated as a subspecies of the widespread Epithelantha micromeris (as E. micromeris subsp. polycephala).
Description
Epithelantha polycephala is a small, tuberculate cactus. Its individual stems are slender — only about 1–2 cm thick — but elongate with age, becoming short cylinders that can reach several centimetres and occasionally as much as 25 cm long. Each stem is densely clothed in tiny, appressed, chalk-white spines that overlap and obscure the green body almost completely, giving a smooth, pebble-like or "button" appearance; new spines at the growing tips are often flushed reddish or pink. The spines are so fine and closely set that a stem can feel almost soft to the touch.
The defining feature is its enthusiastic branching: rather than remaining single, the plant offsets repeatedly from the base and flanks until it builds up a mounded colony of many crowded heads. Small flowers appear near the growing tips in late winter and spring, usually pale pinkish to whitish and modest in size, followed by slender red fruits that are conspicuous against the white bodies.
Distribution and habitat
The species is native to a limited area of the state of Coahuila, in northern Mexico, where it grows on limestone in arid scrub and rocky desert. Like other Epithelantha, it favours cracks, ledges and gritty pockets among rock, often tucked where a little runoff collects but drainage is sharp. In habitat the low, white cushions blend readily into pale limestone and gravel.
As with the whole cactus family, the genus is listed under CITES Appendix II; nursery-propagated plants are legal to own and trade, while collecting from the wild is not.
Cultivation
Epithelantha polycephala is grown much as other button cacti. Give it a very free-draining, mostly mineral mix and bright light — it takes full sun and colours up best there, though light shade in the hottest part of summer does no harm. The main risk in cultivation is overwatering: water thoroughly only once the soil has dried right out, then let it dry again, and keep the plant dry and cool through winter to avoid rot and to encourage flowering. See Watering and Repotting for general technique.
Growth is slow, and the clustering habit means a shallow, wide pot suits an established plant better than a deep one. Because the dense white spination hides the body, check periodically at the base for signs of softening or pests.
Propagation
The species can be raised from seed, which germinates on a warm, gritty surface kept humid until seedlings establish; see Propagation — seed. Its free-clustering nature also makes vegetative increase easy — established clumps can be divided, or individual offsets removed, allowed to callus, and rooted as for other offsets.
Common problems
- Rot — nearly always from overwatering or a mix that holds moisture; heads soften and discolour, often starting hidden within the cluster.
- Etiolation — too little light makes the heads stretch and lose their tight, button-like form.
- Pests — mealybugs can shelter unseen among the crowded heads and dense spines, and red spider mites may attack in hot, dry, stagnant air. See Pests and diseases.
See also
- Epithelantha — the genus overview
- Soil and potting mix · Watering · Propagation — seed · Propagation — offsets · Repotting