The woolly Astrophytums
- Kevin G. Belmonte () - June 6, 2009 - 12:00am

Astrophytums are one of the most popular genus of cacti among collectors globally. In the Philippines, I would venture to speculate that most collectors of cacti have at least one Astrophytum in their collection. Such is the popularity of this genus that many specialist collectors and breeders only grow Astrophytums and nothing else. 

This is a small group of cacti with very attractive yellow flowers that arise from close to the crown of the plant. A typical feature of Astrophytum is the small woolly patches on the skin, though these woolly patches are absent in some varieties (i.e., the variety nudum, which all species have). These are among the most distinct of all cacti. 

For the longest time, six species of Astrophytum were described, namely, A. asterias (the famous sand dollar cactus), A. myriostigma (the famous Bishop’s Cap’s cactus), A. capricorne, A. ornatum, A. coahuilense, and A. senile. A. asterias has a flattened globular body, rather large areoles without spines, and its flowers are yellow with a reddish center. This species has a range from Texas to Tamaulipas and Nuevo Leon, Mexico.

Astrophytum capricorne, also known as the Goat’s Horn cactus because of its long, curling spines, is a more upright grower. It produces a large, yellow flower with a red throat and its body has from sparse to very heavy woolly flecking. For me, this is the species which produces the most beautiful flower in the genus. This plant is from Northern Mexico.

Astrophytum myriostigma is probably the most widespread of the genus in collections. It is a spectacularly different-looking plant. Old specimens really resemble a bishop’s cap, hence its English name. This species has a bluish-tinged body completely covered in white flecking in the typical species, though completely glabrous green variants are also seen without any of the body flecking. Its flowers are yellow without the red throat, and are one of the smaller flowers in the genus. There are numerous varieties of this taxon, each with differences in growth habit, offset production, degree of flecking, number and shape of the ribs. This plant is from the central to northern uplands of Mexico.

Astrophytum ornatum is also known as the star cactus, because of the radiated, star shape of the spines. It is the largest grower in the genus, producing columnar bodies that can reach two feet or more in length in very old specimens. The woolly patches are usually confined to separated bands on the plant body, in contrast to the other species. Its flowers are light yellow without the red throat. This species is from Hidalgo and Queretaro, Mexico.

Astrophytum coahuilense looks very similar to A. myriostigma and is often mistaken for this taxon. It also has a columnar growth and its body is also covered with white flecking. The key difference between A. coahuilense and A. myriostigma is in the flower. In A. coahuilense’s case, the flowers are larger, yellow with a red throat reminiscent of A. asterias and A. capricorne. As its name implies, this species is from Coahuila in Mexico.

The sixth described species is A. senile. It resembles A. capricorne with its spiraling/curling spines, but its body is devoid of woolly patches. Its flowers are similar to A. capricorne, and the plant is also found in Mexico. 

More recently, a spectacular new species of Astrophytum was discovered in Nuevo Leon, Mexico. At first, it was thought to be a new genus of cactus, and was given the genus name Digitostigma. It was given the species name “caput-medusae,” which is derived from  the Latin word caput which means head and Medusa,  the Greek mythological woman-beast whose hair was turned to snakes and whose stare turns anyone who stares back into stone. The plant itself looks so different from the typical Astrophytums, but each of its long, snake-like tubercles is also covered with the white flecking characteristic of Astrophytum. Its flowers also resemble Astrophytum and, in particular, that of A. myriostigma. It readily hybridises with other Astrophytum and is a most welcome addition to this fabulous genus.

I first saw A. caput-medusae in the greenhouse of a fantastic grower of cacti and succulents in Thailand, Khun Deaw. That was back in 2007 when the Cactus and Succulent Society of the Philippines visited Bangkok and its great cactus and succulent growers there. I couldn’t believe my eyes when I was told that this new taxon was, in fact, an Astrophytum. It is a most spectacular plant indeed.

Many Japanese horticulture masters have bred wonderful hybrids from this group. These range from completely “fleckless” specimens to specimens with such heavy flecking that the whole body of the plant seems to be covered in white. The most famous cultivars produced by these Japanese greats and now seen in collections worldwide include Super-Kabuto for the beautifully flecked A. asterias hybrids, and Onzuka, the ultra-white A. myriostigma hybrids.

In terms of growing Astrophytum, in my experience, these require as much direct sunlight as possible. Growing medium should be mineral-based with little or no organic matter added into the mix. Watering well once a week and growing these beauties in porous clay pots work well for me. Fertilizing with a highly diluted balanced fertilizer or a fertilizer low in nitrogen once a month during the growing season (typically from March to November) should result in wonderful specimens which will flower for you several times in a year.

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