For decades the Thornless South American Hybrid Mesquite (most often sold under the names Prosopis chilensis and Prosopis alba) has been a favorite shade tree in Phoenix, Tucson, and other desert cities. Seedlings vary widely in growth habit and appearance, so clonal selections are now popular. The Prosopis juliflora rootstock has slowed down the top growth considerably, and resulted in healthier branching structure with a much more reliable root system that anchors the tree even in strong winds. Prosopis X Phoenix® reaches a mature size of 30 feet tall and wide. In low deserts it is semi-evergreen, with lush green compound leaves. It is reliably cold hardy to 10° F.