Graham's Nipple Cactus or Pincushion Cactus (Mammillaria grahamii) is a common cactus here in Tucson, and these cacti bloom throughout the desert areas here in late spring to summer.

These small cacti are very easy to overlook, except when they are blooming. Their flowers are a lovely rose-pink color, and they ring the cactus tops, sometimes forming perfect, crown-like rings like this one. Whitish radial spines cover the stem "nipples" and one or two dark, hooked spines emerge from each of the "nipples".