[Wikipedia] Range, Habitat, Leaf Anomaly: Fraxinus anomala is a species of ash tree known by the common name single-leaf ash. It is native to the southwestern United States and northern Mexico, where it grows in a number of habitats including desert scrub and chaparral. It is unusual in the genus in that some (though not all) specimens have simple leaves instead of the pinnate leaves more characteristic of the group. (link added by Mary Ann Machi)