Astrophytum myriostigma f. quadricostatum
| Light | Bright light; some protection from the harshest afternoon sun |
|---|---|
| Water | Sparingly; allow to dry fully between waterings, dry rest in winter |
| Soil | Fast-draining mineral mix (see Soil and potting mix) |
| Temperature | Keep above freezing; USDA zones 9b–11 |
| Propagation | Seed (comes fairly true when self-selected); grafting to speed growth |
| Toxicity | Non-toxic to cats and dogs |
Astrophytum myriostigma f. quadricostatum is a four-ribbed form of the bishop's cap cactus, Astrophytum myriostigma, distinguished by its clean, symmetrical square cross-section. Where the typical bishop's cap carries five ribs (giving a pentagonal outline), this selection settles on four, so that a slice through the body reads as a neat rounded square — a look that many growers find especially pleasing.
Care is the same as for the parent species, Astrophytum myriostigma; the notes below focus on what sets this form apart.
Description
Like all bishop's caps, this is a spineless, globular-to-columnar cactus whose skin is dusted with tiny white woolly flecks (trichomes) that give the plant its characteristic grey-white, snow-dusted appearance. The defining trait of the quadricostatum form is its four broad, rounded ribs, which meet at a sharp central apex and produce a square cross-section when the plant is viewed from above or sliced through. The deep vertical furrows between the four ribs are usually more pronounced than in the five-ribbed norm, emphasising the blocky, geometric silhouette.
Young plants show the square habit most clearly. As with other bishop's caps, older specimens sometimes add an extra rib, so a plant grown as four-ribbed may not stay perfectly square for life — part of the fun (and occasional frustration) of growing this form. The funnel-shaped yellow flowers, often with an orange-red throat, emerge from the woolly apex and are identical to those of the ordinary species.
Cultivation
Grow exactly as for Astrophytum myriostigma: bright light, a lean fast-draining mineral mix, and cautious watering with the soil allowed to dry out fully between drinks. Keep the plant dry and cool through winter to encourage flowering and to prevent rot during the dormant season. Bright light helps the plant stay compact and hold its clean geometric form; too little light will stretch it and blur the crisp square outline that makes this form worth growing.
Because the four-rib character is not perfectly stable, growers who want to keep a squared-off line select and grow on the tidiest, most symmetrical seedlings.
Propagation
The four-ribbed form is raised from seed, and seedlings from carefully selected four-ribbed parents come reasonably true, though a proportion will revert to the usual five ribs — expect to rogue out the off-types. Grafting is sometimes used to push seedlings along faster, but bishop's caps grow readily on their own roots, so most growers keep them ungrafted.
See also
- Astrophytum myriostigma — the parent species
- Astrophytum — the genus overview
- Propagation — seed · Grafting · Soil and potting mix · Watering