The Cactoideae are the largest subfamily of the cactus family, Cactaceae, and are widely distributed throughout the Americas.

Cactaceae is the 5th most endangered plant or animal family evaluated globally by the International Union for Conservation of Nature.

All photosynthesis occurs in shoot cortex cells covered by a persistent epidermis and stomata.

Another important characteristic of this subfamily is ribbed stems, which enable the inner cortex to expand radially without breaking the shoot surface to absorb large quantities of water.

[3] As of August 2018[update], the internal classification of the family Cactaceae remained uncertain and subject to change.