Arizona Ash, Velvet Ash
Synonym: Fraxinus pennsylvanica ssp. velutina
Arizona Ash is a fantastic shade tree for Arizona, it has an enjoyable shape and a (relatively) cool shade in summer. However, It does become big, and if you have an aversion to picking leaves in the fall, it might not be the best tree for you.
The male and female flowers are on different trees. The male flowers drop in the spring in large quantities, that can be composted rapidly. The female drops large quantities of one-winged seeds (samara), providing you with a continuous source of seedlings. If you know which is rare, since the tree for sale are generally seedlings, pick the male tree.