Saguaros are found only in the southwestern US, and only in the Sonoran Desert. I often wonder how these desert plants evolved. Many of the cactus and trees in the desert have thick skins to protect them from the hot sun, and to hold water. Saguaros retain water when it rains to the point that you can see them swell. They can go for months without water in the 115 degree heat of the summer. They can only grow when they're young if they are protected from the sun by other plants, so they are often surrounded by palo verde trees, mesquite and other saguaros. The odds are against them, but in spite of that, they are the iconic symbol of the desert southwest. Survival of the fittest.