Desert plants must adapt to survive in the dry conditions found in the environments. Some of the most common adaptations are: Reduction of leaves, turns them in needles or spines for protection. The flat surface of normal leaves helps reduce need for water.
"Development of the stem as a major photosynthetic structure (above right and right). With leaves reduced, photosynthesis has to occur somewhere."(Marietta College)
"Water storage in the stem (above, right). Water is needed for many things; if the plant is to have it available it must be stored." (Marietta College)
"Development of defense structures (above, right, below right). The most common are reduced leaves that take on the form of spines, but chemical defenses are also very common. With less photosynthesis taking place, growth of desert plants is often very slow, and under these conditions it is advantageous for the plants to make greater investments in defense." (Marietta College)
"Coating the plant with a thick waxy cuticle (above and below right). This helps reduce water loss." (Marietta College)
"A dense coating of hairs (trichomes) (below). This slows air moving over the surface of the plant; since air in the desert is very dry any air movement tends to increase evaporation. The trichomes create a microlayer of humid air around the pant, particularly in the vicinity of the stomata." (Marietta College)
"Extensive underground root systems (not shown). These roots can either grow straight down to groundwater, if it is available, or spread out extensively under the surface of the desert. The latter growth form allows the plant to take advantage of short, intermittent rains. Key in this strategy is elimination of competitors' roots; many desert plants inject toxic chemicals into the soil to kill their competitors roots, a phenomenon known as allelopathy." (Marietta College)
Here is an example of a cactus in a desert.