Why do some desert plants have tiny leaves or no leaves at all?

Leaves are useful for photosynthesis, but they also lose water through tiny pores called stomata. In deserts, water conservation is more important than having a large leaf surface, so many plants reduce their leaves, make them small, or replace them with spines. Cacti photosynthesize mainly through their green stems, and many desert shrubs have waxy coatings or fine hairs that slow evaporation. Some plants also use CAM photosynthesis, opening stomata at night instead of during the day. These adaptations let desert flora survive long dry spells.