Mammillaria cactus varieties can span sizes from one inch in diameter (2.5 cm.) to one foot in height (30 cm.). The majority of the readily available species are the ground-hugging variety. As interior plants, growing Mammillaria couldn’t be easier. They need well-draining soil, good light, and warm temperatures. There are over 300 species of Mammillaria, but most you won’t see in the nursery. The tried and true varieties that thrive as houseplants are the easiest to find and provide a glimpse into the Mexican desert. Mammillaria needs a cooling period to promote blooming. Flowers are funnel-shaped in colors of yellow, pink, red, green, and white. The family name stems from the nipple-shaped tubercles which are spirally arranged. The areoles, from which spines grow, can produce hair-like or wooly spines that are either stiff or soft and in a range of colors. The arrangement of spines per species gives a wide variety of appearances as do the many flower colors produced by the plants.