The rattail cactus (Mammillaria pottsii) belongs to Cactaceae (the Cactus family). It is an evergreen perennial herbacious plant that is distributed to Texas in the United States and north Mexico. This cactus grows in arid areas and forms clump. It branches basally, stems are cylindrical, blueish-green, 20 cm high and 3 cm in diameter. Central spines are usually 7 and brown to bluish black. Radial spines are 30-45, white and slender. Flowers are 1.5 cm in diameter, brownish red and not open widely. Fruits are berries and ripen red. The specific epithet is named after John Potts who collected cacti.