Taller perennials are either succulents or have small, leathery leaves that can be shed in times of drought, such as euphorbias. Desert plants face a dilemma. They manufacture the energy they need to survive by combining water, carbon dioxide and sunlight. Most plants can compensate for transpiration by taking up water from the soil as fast as they lose it, but desert plants do not have this luxury. By limiting the size or number of leaves, they also limit the amount of surface from which water vapour can escape.
Many desert plants rely on their stems, which have few pores, to take over the food-producing role.
The ephedra of the Kara Kum Desert in Asia has no leaves and photosynthesis takes place in the stems. Many species open their pores and absorb carbon dioxide at night, when temperatures and evaporation rates are not so high. Some plants, such as gourds, have deep roots to reach water deep down under the sand. Other plants, such as cacti, have roots in the surface-layer of the soil and take up the dew. One way of avoiding temperature rises that could potentially kill the plant is to reflect sunlight.