Astrophytum myriostigma
| Light | Bright light; a little shade from the fiercest afternoon sun |
|---|---|
| Water | Sparingly; let the mix dry fully between waterings, keep dry and cool in winter |
| Soil | Fast-draining mineral mix (see Soil and potting mix) |
| Temperature | Keep above freezing; roughly USDA zones 9b–11 |
| Propagation | Seed (primary); grafting to push seedlings along |
| Toxicity | Non-toxic to cats and dogs |
Astrophytum myriostigma, the bishop's cap (also bishop's miter or bishop's hat cactus), is a typically spineless cactus from the highlands of northern and central Mexico. Its plump, ribbed body is dusted all over with tiny white woolly flecks that lend the whole plant a soft, silvery grey-green cast and its characteristic pointed, mitre-like silhouette.
Description
The bishop's cap is a solitary, slow-growing cactus that begins life as a rounded button and gradually lengthens into a stout column with age. Its most distinctive feature is the number of prominent, sharply defined ribs, usually four to eight, with the typical five-ribbed form giving the plant a symmetrical, star-shaped cross-section that is instantly recognisable from above. The whole body is spineless, with soft felted areoles running along the rib crests rather than any hint of a spine.
What really sets the species apart is the covering of small white woolly flecks, tufts of trichomes, scattered densely over the green skin. These flecks vary from plant to plant: some individuals are so heavily dotted they appear almost chalky white, while others are more sparsely marked and show more of the underlying grey-green. Cup-shaped flowers open from the woolly crown at the top of the plant, glossy yellow and often with a warmer orange or reddish throat, appearing through the warmer months on mature specimens.
Distribution and habitat
Astrophytum myriostigma is native to the highlands of northern and central Mexico, where it grows on limestone slopes and in rocky, well-drained ground among sparse scrub. It is a plant of hot, bright, seasonally dry country, enduring intense sun and long rainless spells in habitat, which is exactly why sharp drainage and a genuinely dry winter matter so much in cultivation.
Cultivation
The bishop's cap is one of the more forgiving Astrophytum for a keen grower, and much of its reputation for being tricky comes down to overwatering. Give it the brightest spot you can offer, with perhaps a little shading from the harshest afternoon glare in high summer to avoid scorching the soft body. Pot it into a fast-draining mineral mix that holds very little moisture; see Soil and potting mix for a suitable recipe.
Water thoroughly during the growing season but only once the mix has dried out completely, then ease right off as the days shorten (see Watering). Through winter, keep the plant cool, bright and bone dry; this dry rest not only prevents rot but also encourages a good flush of flowers the following season. A shallow-to-medium pot suits its slow root system, and an occasional dilute feed in spring and summer is plenty.
Propagation
Because the species is almost always solitary and does not readily offset, propagation is essentially by seed. The seed germinates fairly readily in warm, humid conditions, though seedlings are slow, so many growers use Grafting onto a vigorous stock to speed early growth before returning the plant to its own roots.
Cultivars
Astrophytum myriostigma is enormously variable and has been worked extensively by growers, especially in Japan, giving rise to a wealth of named forms. These include the spot-free green nudum forms, densely flecked and patterned selections, columnar and multi-ribbed variants, and the prized bumpy fukuryu breeding lines. The variety A. myriostigma var. nudum is among the best known.
Common problems
- Rot — by far the commonest killer, caused by too much water, especially in cool weather or a heavy mix. Keep the plant dry in winter and use sharp drainage.
- Etiolation — grown too dark, the body stretches, pales and loses its neat squat shape. More light restores compact growth.
- Scorch — the soft, spineless body can burn if moved abruptly into fierce sun; increase light gradually.
- Pests — watch for mealybugs in the woolly crown and areoles, and root mealybugs at repotting time.
See also
- Astrophytum — the genus overview
- Astrophytum asterias · Astrophytum ornatum — related species
- Grafting · Soil and potting mix · Watering · Propagation — seed