Another popular Mammillaria species is the Mammillaria magnimamma. The stems of the M. magnimamma 'macracantha' will never get larger than about four inches in diameter, but as it ages, it will grow new stems from the base, and eventually form large clumps. Since this specimen will remain potted, it will not clump as readily.
Commonly known as the Mexican Pincushion, its native habitat is Mexico. The scientific name, Mammillaria, means nipple-like, and “magni” means increased size. The reason for its name is self-evident. The white cottony substance in the axils, called wool, is more prevalent in younger specimens. The wool is there for protection from sun and cold. In Phoenix, it needs to be in light shade. Unlike some Mammillaria species, it needs no special protection in winter.
I have several M. magnimamma 'macracantha' in my collection, but no M. magnimamma, which has longer spines and usually produces pink flowers. The 'macracantha' has yellowish flowers. I prefer the look of the spines on the 'macracantha' but I like the flowers of the M. magnimamma more. I understand that there is a wide variation of flower colors on this species, so maybe I'll be surprised when it produces its first flowers.