Astrophytum myriostigma subsp. myriostigma

Astrophytum myriostigma var. nudum is native to the state of San Luis Potosí in Mexico, where it grows in arid and semi-desert environments. It develops on poor, highly draining calcareous soils, often among gravel and rocky outcrops, in areas exposed to intense sunlight and characterized by scarce and irregular rainfall.

The genus name Astrophytum derives from the Greek astron (“star”) and phyton (“plant”), referring to the typical star-shaped form of the stem when viewed from above. The specific epithet Astrophytum myriostigma comes from the Greek myrios (“countless”) and stigma (“dot” or “spot”), alluding to the numerous white trichomes that cover the surface of the plant in the typical form. The Latin term nudum, attributed to the variety var. nudum, means “naked” and describes the characteristic smooth epidermis lacking the usual white speckles.

This cactus belongs to the genus Astrophytum and to the family Cactaceae. It is generally solitary, with a globose stem that tends to become shortly columnar with age, reaching up to about 100-120 cm in height and 5-10 cm in diameter. It differs from the typical form by the almost complete absence of the characteristic white scales or speckles. As a result, the stem displays a smooth and uniform epidermis, with colors ranging from bright green to blue-green or gray-green, sometimes with mauve tones. The cross-section of the stem, when viewed from above, appears star-shaped due to the presence of well-defined ribs, usually five but varying from three to eight. The areoles are small, woolly, and arranged along the margins of the ribs. Spines are absent in mature specimens, while in young plants, when present, they are small and deciduous.

Flowering generally occurs in spring or early summer and is mainly observed in mature specimens, often after about six years of growth. The flowers are solitary and appear at the apex of the stem, reaching a diameter of about 4-6 cm. They are funnel-shaped and pale yellow, with smooth and glossy petals. In some specimens, slight orange shades may also appear at the base of the tepals. The flowers open during the day and may last for several days. After pollination, small dry, globose fruits develop, covered with whitish wool; when mature, they open at the apex forming star-shaped lobes and releasing black seeds.

Generally an easy plant to grow, it has a slow growth rate.

A very well-draining, mineral-rich substrate with little organic matter is recommended, similar to the calcareous soils of its natural habitat. An ideal mix may include fine gravel, coarse sand, pumice, or lava rock with a small percentage of standard potting soil. It is important that the soil allows rapid water drainage to prevent stagnation.

It requires moderate watering during the growing season, from March to October, allowing the substrate to dry completely between waterings. With the arrival of autumn, watering should be gradually reduced, and in winter it should be almost completely suspended, keeping the soil mostly dry.

It prefers very bright positions and tolerates full sun well, especially if gradually acclimated. In very hot climates, light shading during the hottest hours of summer is recommended to prevent sunburn of the epidermis. During winter, it is advisable to keep the plant in a cool, dry, and well-lit environment; under these conditions it can tolerate brief drops in temperature down to about -5 to -7 °C (23–19 °F), although in cultivation it is preferable not to go below freezing.

It is advisable to use a fertilizer specifically formulated for cacti, low in nitrogen and with a good content of phosphorus and potassium, diluted in the watering water once a month. Fertilization should be suspended during the winter dormancy period.

Repotting should be done only when necessary, generally every 2–3 years, preferably at the beginning of spring as the plant resumes growth. It is recommended to use pots slightly larger than the previous one and a very well-draining substrate rich in mineral components.

It is not generally considered a toxic plant for humans or pets. Thanks also to the absence of spines (in adult specimens), it can be grown indoors without particular problems.

It is generally a hardy plant. However, it may occasionally be attacked by common cactus pests such as mealybugs, which settle in the areoles or among the apical wool, and more rarely scale insects. Spider mites (red spider mites) may also appear, especially in very hot and dry environments. Root mealybugs can develop in the soil and may be difficult to detect. The most common problem, however, is rot, usually caused by excessive watering, poor ventilation, or poorly draining substrates.

A useful tip is to use pots that are fairly deep but not too wide, allowing the roots to develop without retaining excessive moisture in the substrate.

It is mainly propagated by seed, as the plant usually grows solitary and does not produce offsets. Sowing is carried out in spring using a light, well-draining substrate kept slightly moist until germination and placed in a warm, bright environment. It is worth noting that young seedlings grow slowly and generally require several growing seasons before developing the typical ribbed form. In specialized cultivation, grafting onto other cacti is sometimes practiced to accelerate growth, especially in the early stages.

This form is known in Japan as “Hekiran”, a term used among collectors to indicate specimens lacking the typical white speckling.