Answer: Take a look at desert trees, such as mesquite, palo verde, and ironwood. What do their leaves look like? Basically, they're very tiny leaves, right? Have you seen photos of trees from tropical areas, such as the rain forest? They have much larger leaves, sometimes huge leaves. Desert trees have adapted their tiny leaves to reduce the amount of surface area that the sun hits, and therefore reduce the amount of transpiration, or water loss. In the rain forest, it's the opposite. There's such a dense canopy of foliage, that plants underneath have to have large leaves, therefore more surface area, to capture as much sunlight as they can.
Other desert plants have made adaptations for our limited rainfall, harsh sun, drying winds, and alkaline soil. I don't have any website URLS where you'd find this type of information. I suggest you go to the library and ask the reference librarian to show you the appropriate resources. Most AZ libraries have a good selection of books on desert topics.
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