Mammillaria takes its name from the Latin for nipple, a precise if unglamorous reference to the rounded tubercles that spiral across each stem. The genus spans from the American Southwest through Central America to Venezuela, encompassing spherical species and cylindrical ones, solitary plants and colonies that spread over 3 feet across. What they share is a capacity for small, funnel-shaped flowers — white, yellow, pink, or red, often with a dark stripe down each petal — that ring the crown in a neat halo.

As houseplants, they want bright direct light, sharp drainage, and benign neglect through winter. Keeping them cool and bone-dry from roughly November through February encourages flowering the following spring. Repot every 2 to 3 years as growth warrants, and propagate by dividing the small offsets that cluster at the base. The spines are sharp enough to earn respect. Some wild species are endangered from over-collection, which makes growing named cultivars from reputable nurseries the responsible choice.