Astrophytum coahuilense
| Light | Bright light; a little shade from the harshest afternoon sun |
|---|---|
| Water | Sparingly; let the mix dry fully between waterings, keep dry 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 speed seedling growth |
| Toxicity | Non-toxic to cats and dogs |
Astrophytum coahuilense is a globular-to-columnar, spineless cactus from the Mexican state of Coahuila, closely allied to the bishop's cap (Astrophytum myriostigma). It is distinguished by an almost invariably five-ribbed body cloaked in dense white flecking, and by yellow flowers with a red throat that give rise to a distinctive fig-like fruit which splits open from the base.
Description
Astrophytum coahuilense forms a solitary, grey-green body that is squat and globe-shaped when young, becoming more columnar with age. It is almost always sharply five-ribbed, giving the plant a clean, geometric outline much like its relative Astrophytum myriostigma. The entire surface is densely covered in tiny woolly flecks (trichomes), so heavy that the plant often appears chalky white or silvery from a distance — one of its most reliable field characters. Like other bishop's-cap types it is completely spineless.
The flowers open at the rib crests near the crown, are funnel-shaped and clear yellow, and carry a warm red or orange throat at the centre — a feature that helps separate it from typical A. myriostigma, whose flowers are usually plain yellow. After flowering it sets a rounded, greenish, somewhat fig-like fruit that is another good identifier: rather than opening at the top or splitting down the side as in some relatives, the ripe fruit tends to split open from the base, exposing the black seeds.
Distribution and habitat
As the name suggests, Astrophytum coahuilense is centred on the state of Coahuila in northern Mexico, its range extending across southwestern Coahuila and into adjacent Durango. It grows on sunny limestone slopes and flats with mineral-rich, chalky soils in arid scrub, typically at moderate elevations of roughly 1,100–1,600 m. It endures strong sun, considerable summer heat, and a long, dry, cool winter rest. Historically it has been treated as a variety or subspecies of Astrophytum myriostigma (see the synonyms), and many growers still think of it as the "Coahuila form" of the bishop's cap, though it is now widely recognised as a species in its own right.
Cultivation
This is a rewarding, undemanding plant for anyone who can give it sun and a truly gritty mix. Grow it in bright light — near-full sun suits it, with perhaps a little shading from the fiercest afternoon glare in very hot climates to avoid scorching. Use a fast-draining mineral mix (see Soil and potting mix); a heavy pumice, grit or lava content keeps the roots healthy and encourages that dense white flecking.
Water thoroughly during the warm growing season, then let the mix dry out completely before watering again (see Watering). In winter give it a cool, essentially dry rest — this both protects it from rot and helps trigger flowering the following year. Keep it above freezing; it is happiest in the range of USDA zones 9b–11 and is best grown under cover or indoors wherever hard frosts occur. A shallow-to-medium clay or plastic pot with a good drainage hole is ideal.
Propagation
Astrophytum coahuilense is grown almost entirely from seed, which germinates readily when fresh — sow onto a sterile mineral mix and keep warm and humid until the seedlings establish (see Propagation — seed). Because it is solitary and rarely offsets, division is not usually an option. Growers wanting to speed up slow seedlings, or to bulk up a special clone, sometimes graft young plants onto a vigorous stock (see Grafting); grafted plants grow and flower faster but take on a somewhat different, plumper look.
Common problems
- Rot — by far the commonest killer, caused by too much water, a mix that holds moisture, or watering during the cold winter rest. Keep the medium gritty and err on the dry side, especially in cool weather.
- Etiolation — grown too dark or too warm and wet, the body stretches, loses its neat five-ribbed form and produces sparse flecking. Give it more light.
- Corky scarring — cold, wet conditions or physical damage can leave permanent brown patches; largely cosmetic but avoidable with good culture.
- Pests — watch for mealybugs (including root mealybugs) and the occasional red spider mite; inspect the crown, base and roots at repotting.
See also
- Astrophytum — the genus overview
- Astrophytum myriostigma — the closely related bishop's cap, of which this was long treated as a variety
- Grafting · Soil and potting mix · Watering · Propagation — seed