The Bishop’s Cap, or Star Cactus, (Astrophytum myriostigma) is a spineless, five-ribbed cactus that is easy to grow in Phoenix, but it’s not a common landscape cactus here. Most end up as potted specimens because of the unusual shape and coloring. I put this specimen in the garden just this year, and it’s doing very well and flowering regularly. I also have several more in containers that may also go into the garden next spring.
The A. myriostigma will not retain the bishop’s cap shape as it ages. It becomes columnar, and can reach about two feet at maturity. The A. myriostigma can have between three to eight ribs, but five, like the one in the photo, is the usual number. Collectors love finding specimens with differing numbers of ribs.
The cactus has little wooly areoles located on the ribs, but no spines. The whitish scales, or flecks, cover the skin of the cactus and act as a natural sunscreen. The scales sometimes flake off, giving the cactus a mottled appearance. Pale yellow flowers come in spring and summer, and have a very nice fragrance. They last about four days, opening during the day and closing at night.
As with so many cacti, it is important to keep the A. myriostigma dry in winter to prevent root rot. It can take full sun in Phoenix after acclimation, and is fertilized in summer—if fast growth is wanted. If placed in light shade, the cactus becomes greener and doesn't grow as fast.
The Astrophytum genus is small, containing only five known species. Four species are readily available at cactus nurseries, and there are endless varieties and hybrids, especially of the A. asterias. All the Astrophytum species are native to the central and northern plateaus of Mexico, where the Tarahumare Indians used the A. myriostigma as a peyote substitute. The cactus does contain unspecified alkaloids, but probably not enough to produce any hallucinogenic “magic carpet rides” for the more daring collector.