Cactus or cacti belong to the succulent plant family Cactaceae, native to the Americas. They come in a wide range of sizes, with a maximum recorded height of 19.2 m. The smallest is only about 1 cm in diameter at the time of maturity.

They are distinctive plants and have a wide range of anatomical and physiological features for conserving water. Cacti have very small leaves, microscopic in many cases, which help in reducing the loss of water through transpiration.

Cacti have enlarged green stems that contain chlorophyll which is necessary for plant life. The stems also carry out photosynthesis. Their thick, waxy cuticles have special water-retention properties.

Most of these cacti have very shallow roots, which spread out wide, close to the surface of the ground to absorb water — another way in which they survive in a harsh, arid environment.