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. Around 80% of cactus species belong to this subfamily. The genera of the Cactoideae are characterized by microscopic foliage leaves. 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.

Cereinae is a subtribe of cacti in the tribe Cereeae, subfamily Cactoideae. It is one of the three subtribes into which the tribe Cereeae is divided, the others being Rebutiinae and Trichocereinae.