Mesquite trees (Prosopis genus) are common sights across the arid and semi-arid regions of the American Southwest, known for their resilience in harsh climates. These adaptable plants, belonging to the pea family (Fabaceae), range in form from sprawling shrubs to small, rugged trees. Visually identifying a mesquite relies on a combination of characteristics, including its overall structure, the intricate details of its foliage, and its highly distinctive reproductive parts.
Overall Growth Habit and Bark
The mesquite typically grows as a small tree or a multi-stemmed, asymmetrical shrub, often reaching heights between 15 and 30 feet, though some specimens can grow taller with sufficient water. Its canopy is frequently irregular, offering a filtered shade that is often wider than the tree’s height, especially in open areas.
The bark of a mature mesquite is rough and thick, ranging in color from reddish-brown to dark gray or nearly black. Older trunks develop deep furrows, scales, and a shaggy appearance, which provides insulation against temperature extremes. Younger bark may be smoother and lighter, but it quickly develops the characteristic fissured roughness as the plant ages.
Leaves, Branches, and Thorns
Mesquite foliage is deciduous and finely detailed, appearing as a light green to gray-green color. The leaves are complex, specifically described as bipinnately compound, meaning the main leaf stalk branches twice to hold numerous small leaflets. These leaflets are small and narrow, giving the canopy a delicate, fern-like appearance.
The branches often grow in a somewhat angular or zigzag pattern, which is noticeable on young twigs. Along these branches, mesquites are typically armed with stout, sharp thorns. These thorns usually appear in pairs at the leaf axils and can range in size from a half-inch up to two inches long, though some cultivated varieties may be thornless.
Flowers and Seed Pods
Mesquite trees produce small, fragrant flowers that cluster together in dense, elongated spikes or catkins. These flower clusters are generally yellowish-green to pale cream or white and appear on the tree in the late spring or early summer.
The most recognizable feature of the mesquite is its fruit, a long, bean-like pod classified as a legume. These pods are green when young and ripen to a tan, light brown, or purplish color. They vary in shape from straight and flattened to curved or even tightly coiled, depending on the specific species. The pods are typically sweet and edible, containing hard seeds encased in a spongy, nutritious pulp.
Identifying the Main Species
Differentiating the three most common native species in the American Southwest requires close attention to the leaves and pods.
Honey Mesquite (Prosopis glandulosa)
The Honey Mesquite is distinguished by its long, straight, or slightly curved pods that can reach up to nine inches in length, and its smooth-surfaced leaves. This species also tends to have longer, more slender thorns compared to its relatives.
Velvet Mesquite (Prosopis velutina)
The Velvet Mesquite is named for the fine, velvety hairs covering its leaves and young branches, which give the foliage a grayish-green hue. It typically grows into a larger tree with a darker, rougher, shaggier bark than the honey mesquite. Its pods are straight to slightly curved, similar to the honey mesquite, but its leaflets are often smaller and more numerous.
Screwbean Mesquite (Prosopis pubescens)
The Screwbean Mesquite is the easiest to identify due to its unique fruit, which is a tightly coiled, screw-like pod. This species is generally smaller and more shrubby than the others, and it often has a shaggy, flaky bark.