How do plants like Cactus survive in the Desert

Cacti have never lost their leaves completely; they have only reduced the size so that they reduce the surface area through which water can be lost by transpiration. In some species the leaves are still remarkably large and ordinary while in other species they have become microscopic but they still contain the stomata, xylem and pholem Certain cactus species have also developed ephermeral leaves which are leaves that last for a short period of time when the stem is still in its early stages of development. A good example of a species that has ephemeral leaves is the prickly pear.
The bodies of many cacti have become thickened during the course of evolution, and form water-retentive tissue and in many cases assume the optimal shape of the sphere.