Cercidium Species, Little Leaf Palo Verde, Foothill Palo Verde

No thorns on the trunk, but the branch tips have them.
Green-yellow trunk, small leaves, irregular quasi growth structure.
...Read MoreOccasional deep watering for better foliage.
Provides just about the right amount of shade for some cacti.

A comparison between the flowers of five Palo Trees
--The Mexican Palo Verde (Parkinsonia aculeata), the upper petal starts out with red dots that eventually grow bigger and turn the entire top petal to red.
--The Palo Brea (Parkinsonia praecox), the upper petal has smaller & fewer red dots than the Mexican Palo Verde (P. aculeata) that don't grow bigger.
--The Blue Palo Verde (Parkinsonia florida), the upper petal is always a solid yellow just like the other four petals.
--The Little Leaf Palo Verde (parkinsonia microphylla), the upper petal is solid, all white, and the remaining petals are yellow.
--The Palo Brasil (Haematoxylum brasiletto), has flowers similar to Parkinsonia sp., and the top yellow petal has red dendritic streaks.

I've seen this growing in the wild at Oracle Junction, AZ; Oro Valley, AZ; Kearney, AZ and on the 'El Camino Del Diablo Trail' (Devils' Highway) that runs between Ajo and Wellton, Arizona in the Cabeza Prieta National Wildlife Refuge.