Mesquite trees are an iconic feature of the American Southwest landscape. Mesquites are indigenous to Arizona, but the presence of multiple species complicates the full picture. Some varieties are native to the Sonoran and Chihuahuan deserts, while others were introduced from South America. Understanding these distinctions is important for appreciating the local ecology and the differences seen in urban landscaping. The native mesquite is a highly adapted desert species, contrasting sharply with ornamental varieties often planted for rapid growth.
Arizona’s Truly Native Mesquite Species
Arizona is home to three indigenous mesquite species, with the Velvet Mesquite (Prosopis velutina) being the most widespread native variety in the central and southern parts of the state. This tree gets its common name from the dense, short, gray hairs that cover the young foliage and branches, giving them a soft, velvet-like texture. Mature Velvet Mesquites can reach heights of 30 to 50 feet in favorable conditions and are characterized by dark brown, rough, and deeply fissured bark. They thrive at elevations below 5,000 feet, often forming dense woodlands called bosques near washes and floodplains where water is more accessible.
The Honey Mesquite (Prosopis glandulosa) is another native species, though its distribution is more varied, and it readily hybridizes with the Velvet Mesquite, creating intermediate forms. Honey Mesquite typically possesses a more weeping growth habit and shinier, less-hairy foliage than its velvet counterpart. A third native, the Screwbean Mesquite (Prosopis pubescens), is instantly identifiable by its distinctively coiled seed pods, which resemble a tightly wound spring. These native trees are deciduous, shedding their leaves in response to cold temperatures or severe drought to conserve moisture.
The Non-Native Species Causing Confusion
Confusion regarding mesquite’s native status often stems from the widespread planting of non-native species for landscaping purposes. The Chilean Mesquite (Prosopis chilensis) is one of the most common ornamental introductions, originating from South America. It was favored in urban environments for its fast growth rate and its delicate, lacy crown of foliage, which can appear nearly evergreen during mild Arizona winters.
Another South American import is the Argentine Mesquite (Prosopis alba), which is noted for its vigorous growth and sometimes very large thorns. These non-native trees and their hybrids are sold in nurseries because they offer a larger canopy and faster shade than native varieties. Visually, the South American mesquites often lack the velvety pubescence of the native species, and they maintain their leaves longer into the winter, which is a key distinction from the truly deciduous native Arizona mesquites.
Essential Role in Arizona’s Desert Ecosystems
Native mesquite species play a fundamental role in the ecology of Arizona’s arid and semi-arid environments. Their most remarkable feature is their root system, which includes a taproot that can reach extraordinary depths to access groundwater, sometimes documented at over 160 feet below the surface. This adaptation classifies the mesquite as a phreatophyte, a plant that draws its water supply from permanent subterranean sources, allowing it to survive prolonged periods of drought.
As members of the legume family (Fabaceae), mesquites also possess the ability to fix atmospheric nitrogen into the soil through a symbiotic relationship with bacteria in their roots. This nitrogen-fixing process enriches the otherwise nutrient-poor desert soil, providing a localized benefit to surrounding plant life. The shade provided by their canopies creates a cooler microclimate on the desert floor, which is important for the germination of other plants and the sheltering of various small animals.
The mesquite tree serves as a crucial food source and habitat for a variety of native wildlife. The seed pods, often referred to as mesquite “beans,” are a high-protein food source for animals like coyotes, deer, and numerous rodents, especially during the late summer and fall. Birds utilize the branches for nesting and perching, while the flowers provide nectar for bees, contributing to the production of high-quality mesquite honey. This comprehensive function in stabilizing soil, fixing nitrogen, and supporting desert fauna underscores the native mesquite’s importance.