Where are the stomata on cactus?

The stomata on cactus plant are contained in the skin of the cactus stem. The cacti which are considered more primitive, such as Peireskia and Opuntia, also have stomata in their leaves. The more highly desert adapted cacti have no leaves so they photosynthesise through their skins. Often the stomata are heavily protected by physical adaptations such as waxes or pits in the skin. They also display "behavoural" adaptations such as opening only at night to reduce water loss even further.