The Chilean mesquite tree (Prosopis chilensis), native to South America, is popular in the Southwest for landscaping because of its dome-shaped canopy of leafed branches. The leaves of this tree are particularly interesting and showy, giving the tree much of its ornamental appeal.
Chilean mesquite trees have bipinnately compound leaves. Rather than being single-bladed, this type of leaf has a complex formation, with a number of small leaflets attached to a central axis known as a pinnae. The leaflets look like flattened needles and grow opposite each other. This pattern gives the foliage a feathery appearance, resembling that of a fern.
The number of leaflets that grow on the pinnae of the Chilean mesquite tree varies. On some, there may be as few as 10 pairs of leaflets growing opposite each other. On other pinnae, there can be as many as 29 pairs of leaflets.
Types of Mesquite
A close relative of the Chilean mesquite tree is the Argentine mesquite. This type of mesquite has many of the same characteristics of the Chilean mesquite, but there is an easy way to tell the two apart. On the Argentine mesquite, the leaflets growing on the pinnae are much closer together than on the Chilean tree. In addition, the Argentine mesquite has almost twice as many leaflets per pinnae as the Chilean mesquite.
The leaves of the Chilean mesquite produce a great deal of shade. Overlapping in great numbers the leaves form a canopy that blocks out much of the sunshine, an asset in the hot and sunny Southwest. In addition, the Chilean mesquite tree appears lush from a distance, with the green leaves providing color in desert landscapes.
The Chilean mesquite is a semi-deciduous tree, meaning that it will shed only some of its leaves during the winter months. The tree tends to lose more leaves in desert regions where the winter temperatures are a bit chillier, such as Tucson and Las Vegas. The remaining leaves of the Chilean mesquite will fall off in the spring, but then quickly grow back duirng the same season.