Mammillaria — 46 species

Mammillaria is one of the largest cactus genera, comprising globe-shaped or cylindrical plants densely covered in spines and often ringed by a crown of small, jewel-like flowers in pink, red, or white. Native to Mexico and the southwestern United States, they thrive in full sun and need very infrequent watering — allow the soil to dry completely between drinks and ensure excellent drainage to prevent rot. The genus is non-toxic to cats and dogs, making it one of the safer cactus choices for pet households, though the sharp spines still pose a physical hazard.