The Gymnocalycium genus contains around 80 species that grow in South America. There is a tremendous variety among the genus, both in spine formation and skin color, which can range from a blue-green to olive green, brown, gray and even a purple shade. Because many of the species flower freely and are easy to care for, they are popular with collectors. The cacti in this genus are called Chin Cacti because of the indentation just under the areole that resembles a chin. The spines on many of the species in this genus resemble spider legs, so another common name for the genus is Spider Cacti.
I have about 10 different Gymnocalycium species. I’ve tried to include a variety of spination and coloration as well as flower color. I like this particular species, G. mesopotamicum, because the spines have the distinct “spider” look common in so many Gymnocalycium, and because the skin color has a slight teal hue.
G. mesopotamicum originates from Argentina, and does well in the Phoenix area in light shade. However, it is frost sensitive, and does better if not exposed to temperatures lower than 50ºF. It is a summer grower, and it produces a medium sized white flower, usually in July. The only trick with this genus is the cacti must have at least six hours of very bright light each day to produce flowers. Because of the shade needs in Phoenix, it’s necessary to locate each Gymno for both bright light and sun protection.