Three trees that illustrate the breadth of diversity within the genus Acacia are Leather Leaf Acacia, (A. craspedocarpa), White Thorn Acacia, (A. constricta) and Palo Blanco, (A. willardiana). Two are native to the desert southwest, Palo Blanco and White Thorn while Leather Leaf is an Australian relative. Palo Blanco and Leather Leaf are unarmed (thornless), while Whitethorn, as the name implies, has conspicuous, thin white thorns, although even this species can at maturity revert to thornless growth. All three are relatively small-stature trees, ideal for accent or "foundation" planting, screening or in tight or narrow locations.

Leather Leaf Acacia is an excellent, descriptive name for this Australian native. Its dense, upright branches form an erect, compact head that make it an ideal privacy screen or windbreak shrub. It can also be used as a background or foundation plant or as individual specimens. Mature plants may reach 9' to 12' and be 6' to 8' wide. It is used primarily as a large shrub or small tree in southwestern landscape designs where it can be planted closely to form a dense hedge or as individual specimens or small groupings.

Leaves are gray-green in color and slightly oval shaped with densely netted veins. In Spring individual, bright yellow, elongated rod flowers are produced. Tan-colored, flat, 2" long pods develop from the flowers. Leather Leaf Acacia is moderately cold hardy and grows well in full and partial sun. It will tolerate a variety of soils but does best in well-draining soils.

Established plants are highly adapted to harsh summer conditions and can survive without supplemental irrigation. Watering once a month will ensure limited growth but more frequent irrigation is needed to achieve optimal growth, appearance and flowering. This plant grows slowly and in some landscape applications it may be desirable to install larger container sizes (15 gallon to 24" box) to get more immediate impact.

White Barked Acacia and Palo Blanco are the two common names associated with Acacia willardiana. Palo Blanco has a slender, upright form that matures to about 10 to 25 feet tall and 10 feet wide. Because of its relatively small size, this delicate, weepy desert tree is used as an accent, in entry areas and patios or to cast shadows against a wall or building. It is native to Sonora Mexico where it is found on rocky hillsides in the transitional areas between arid and semi arid climates at 400 to 800 feet. Leaves are made up of a thin 4" long midrib that divides to form two leaflets about 1" long. Each leaflet then bears ten tiny leaflets. The petiole is a flattened phyllode less than ¼ inch wide and 2 ½ to 3 ¼" long. Palo Blanco is the only Sonoran desert plant (and only American plant) with phyllodic petioles. The canopy on even fairly mature specimens is almost transparent providing only very modest shade. White to cream-colored, spike flowers appear in spring and mature into dark brown, 3" to 8" long pods over the summer. Trees are deciduous and grow best in full sun and well-drained soils. Palo Blanco grow slowly and require little or no pruning once mature shape is established. They are reported to be cold hardy to temperatures in the mid 20's but have been severely damaged by temperatures in this range in some desert locations.

Besides the lacy form of this tree, its other distinguishing feature is the peeling, papery, silver-white bark. The form and texture can be enhanced with creative landscape lighting or by planting against a contrasting background. Its peeling bark, beautiful silhouette and small stature make Palo Blanco an ideal accent tree in arid landscape designs.

With its lush green foliage and conspicuous ½" long bright white thorns, A. constricta is a study in visual contradiction, being at once inviting and cautioning not to come too close. In summer the finely divided (4 to 16 pairs of leaflets), lush green foliage stands out against the gray to mahogany-brown bark. Thorns are borne in pairs and originate at leaf nodes along branches. Thorns are bright white and easily visible, adding to the interesting texture of the tree's canopy. Yellow-orange, fragrant, ball-shaped flowers first appear in spring and again in late summer through the fall months (depending on seasonal rains). Pods are 4" long, curved, reddish brown in color and constricted or narrow between each seed. Trees are cold hardy to 0 degrees F and are both drought and cold deciduous.

Native to Arizona, and Sonora, Mexico, it is found at elevations from 0 to 1800 feet, along washes and arroyos where runoff compensates for the lack of rainfall. In these natives setting it grows at a moderate rate to a large shrub or small tree. In its natural habitat you may find the tree unarmed. In the landscape, reports suggest a range of mature sizes from 10 to 18' tall and as wide. They can be grown in a spreading shrub form or pruned into graceful single or multiple trunk specimens. White Thorn Acacia will tolerate shallow, alkaline soils but will thrive in full sun and well-drained soils. Established trees can be naturalized to survive on annual rainfall in most desert locations but are most lush and produce more flowers if irrigated deeply once a month during spring and summer.

The Seri Indians used the leaves, mashed seeds and roots of A. constricta for stomach ailments, skin rashes and medicinal teas.

With a form and stature similar to A. smallii, White Thorn makes an excellent accent tree with its form, color and fragrant flowers. Specimens can be planted singly or in small groupings. Planting in combination with semi-evergreen trees and shrubs will soften the visual impact of White Thorn Acacia when it is dormant. They are also used to replant disturbed desert or as a transition tree between landscaped areas and the surrounding desert. Trees planted close together will form a loose, informal hedge that provides screening and security.