Barrel cactus is not listed as a dominant or codominant species in available publications. Mule deer in the Sonoran Desert readily consume barrel cactus fruits. Barrel cactus is a native stem succulent that is barrel-shaped or sometimes columnar with rarely more than one stem. Barrel cactus has 20 to 28 ribs. The spines are dense, somewhat obscuring the surface of the stem.
Flowers form on growth of the current season near the stem apex.
Horizontal roots originated from the root crown and were very shallow. Roots were often exposed after rain storms. Limiting factors for germination of barrel cactus seeds are temperature and light. The cortex thickens with age, so older individuals may be more resistant to fire than younger ones. Taller individuals are more likely to survive fire because the apical meristem may be above flame height.