Astrophytum myriostigma var. nudum
Astrophytum myriostigma var. nudum is a naked, flecking-free form of the bishop's cap cactus, Astrophytum myriostigma. Where the typical species is dusted all over with tiny white woolly scales (trichomes), the nudum form lacks them entirely, leaving a smooth, green body. Growers prize it both for that clean, unmarked look and as a starting point for further cultivar breeding.
Description
Like the parent species, nudum is a slow-growing, mostly spineless cactus that forms a rounded, star-shaped body, usually with five broad ribs (though four- and multi-ribbed plants occur). What sets it apart is the complete absence of the fine white flecking that gives ordinary A. myriostigma its speckled, "star-dusted" appearance. Instead the epidermis is a solid, deep green. The areoles along the rib edges may carry a little wool, but the body surface itself stays bare. Yellow flowers, often with a reddish throat, open from the crown in the growing season, just as they do on the type plant.
Because the flecking is a heritable trait, nudum comes fairly true from seed, and the trait can also be combined with other selected characters (extra ribs, compact bodies, and so on) in breeding work.
Distribution and habitat
As a selected form rather than a wild population, nudum has no distinct range of its own — it derives from Astrophytum myriostigma, which is native to northern and central Mexico, where it grows on rocky limestone slopes in seasonally dry scrub. The naked form is maintained in cultivation and by hobbyist seed lines.
Cultivation
Care is exactly as for the parent species; see Astrophytum myriostigma for full detail. Give it bright light — nearly full sun once acclimatised, with a little shading from the fiercest afternoon summer sun to avoid scorching the green skin, which lacks the sun-reflecting white coating of the type. Plant in a gritty, fast-draining mineral mix and water thoroughly during the warm growing season, letting the soil dry out completely between waterings. Keep it dry and cool through winter to encourage a proper dormancy; see Watering for seasonal rhythm. Protect from frost.
One thing worth noting: without the white trichome layer, a nudum body can be a touch more prone to sunburn if moved abruptly into strong light, so bring it on gradually in spring.
Propagation
Seed is the usual route and the trait largely carries through, making nudum straightforward to raise as a seed strain. As with all Astrophytum, seedlings are slow, and growers in a hurry sometimes speed them along by grafting onto a vigorous stock before returning selected plants to their own roots.
See also
- Astrophytum myriostigma — the parent species (bishop's cap)
- Astrophytum — the genus overview
- Grafting · Soil and potting mix · Watering · Propagation — seed