Combining the growth rate and adaptability of Thornless Mesquites and the structure and appearance of the Desert Ironwood, Mexican Ebony (Pithecellobium mexicanum)   is a versatile and underutilized desert landscape tree.   With small gray-green leaflets, an open canopy and smooth, chalky gray trunks, its appearance mimics Desert Ironwood.  The growth rate approaches that of Thornless Mesquite. In warm micro-climates, it retains most of its foliage, through the desert winter months. The lacy leaf canopy, smooth, curving, chalky gray trunks make Mexican Ebony, also called Palo Chino, a tree that can substitute for or be inter-planted with Ironwoods.  Unlike Ironwoods, it can be planted in a wide variety of landscape settings including turf areas or mixed with under-story plantings that require regular, year round irrigation.
 
The tree is native to the Mexican states of Sonora, Sinaloa and southern Baja. In natural settings trees are found growing in arroyos, desert slopes and valley floors. They cannot be naturalized in desert landscape settings and will require some summer irrigation. Both the small leaflets and immature bark are a pale gray-green. The bark fissures and darkens slightly as trunks and branches mature. It is hardy to 15 F and armed with small cat-claw like thorns. Cream colored blooms appear in March and April with 1 to 3 inches long, thick brown pods maturing by mid-summer.  In the desert, trees mature to about 20' tall and 15' wide.    In landscape settings, with the benefit of regular irrigation, fertilization   and well-drained soils, they may grow larger.
 
Mexican Ebony provides filtered shade that is ideal for promoting the growth and flowering of under-story plantings.  With its striking color and form it can be used as an accent tree, at entry monuments or any application where Ironwoods would be attractive.   They work well as a perimeter planting or as a transition tree from landscaped areas to undisturbed desert.
 
Pithecellobium pallens (common names Tenaza or Ape's Earring) is another specie that could be used more widely in the southwest. The branches are long, upright and straight, giving the tree a vertical, almost columnar growth habit.  Small thorns are found on juvenile trees but, as trees mature, the new growth is nearly thornless.  Leaves resemble those of Sweet Acacia with multiple small, light green leaflets that produce an open canopy and filtered shade. Its more columnar growth allows its use in side yards, as a screen planting or hedge, between buildings, along fences or other locations where space is limited. Field evaluations showed Tenaza was hardy to about 15 F, sustaining only limited leaf burn at this temperature.

Some literature suggests that P. pallens grows as a large shrub, maturing at 10' to 15' while others report mature trees at 20' to 30'. Its growth rate and mature size have not been fully evaluated in desert landscape conditions. Experience to date, with trees in landscapes, tends to support the larger mature height. It has a fairly fast growth habit and takes full sun. From Spring to Fall (generally after rains or irrigation) clusters of creamy white, fragrant, powder-puff flowers, similar to those on Fairy Duster (Calliandra eriophylla), cover the branches. These flower displays are very showy and add to the value of Tenaza as an accent or specimen tree.   Trees require regular supplemental irrigation during the hot desert months. Without summer irrigations trees will go summer deciduous.

Landscape professionals familiar with Texas Ebony (Pithecellobium flexicaule), will find  Mexican Ebony and Tenaza very different from their better know relative.   With their unusual color, fast growth habits, unique structure and comparatively smaller stature.