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Astrophytum is a genus of cacti native to Mexico, with an estimated six to 10 known species. In addition, a number of cultivars have been developed for the nursery trade. These cacti have a distinctive star shape when viewed from overhead, explaining the genus name, which translates as “star plant.” A number of common names including sand dollar cactus, star cactus, bishop's cap cactus, and living rocks are used to refer to members of this genus. People should be aware that “living rocks” is a term used in reference to a number of other plant genera as well.
The Astrophytum species start out as rounded, globular specimens when they are juvenile. As they mature, they develop a distinctive starred or rounded shape with large, prominent ribs. Flowers are produced at the top of the plant and are typically bright yellow. After flowering, a large hairy fruit develops. Flowering frequency varies, depending on the climate and the environment.
These cacti are very easy to grow, making them suitable for beginners just getting started with cacti. For indoor gardening, they can be grown alone in containers or paired with other cacti and succulents. They need a well-drained soil medium, because they are very susceptible to rot. Astrophytum cultivars are produced both with seeds and grafting, and are often readily available at nurseries and stores that specialize in succulents and cacti. People interested in growing cacti may also be able to make exchanges with other gardeners.
People in desert climates can also grow Astrophytum outdoors. These plants are adapted to the varying extremes of the desert, from high daytime temperatures to frosty nights, and they tolerate dry conditions very well, like other cacti. Gardeners should be careful to avoid over-watering their Astrophytum cacti in the garden. For succulent gardens, rockeries, and other low-water gardens, star cacti can be an excellent choice. Outdoor gardening in containers is also possible.
Sources for interesting cultivars can include mail order catalogs, as well as enthusiast clubs for people who grow cacti and succulents. People all over the world breed Astrophytum species and have developed plants with a number of unique characteristics and traits. Enthusiasts are often eager to share their cultivars with people who are interested in cacti, and may also be able to provide information about the history of particular cultivars and crosses.