Mesquite is a common name for several plants in the genus Prosopis, which contains over 40 species of small leguminous trees. They are native to the southwestern United States and Mexico (except the creeping mesquite, which is native to Argentina, but invasive in southern California). The mesquite originates in the Tamaulipan mezquital ecoregion, in the deserts and xeric shrublands biome, located in the southern United States and northeastern Mexico. It has extremely long roots to seek water from very far under ground. The region covers an area of 141,500 km2 (54,600 sq mi), encompassing a portion of the Gulf Coastal Plain in southern Texas, northern Tamaulipas, northeastern Coahuila, and part of Nuevo León. As a legume, mesquite is one of the few sources of fixed nitrogen in the desert habitat.
This tree blooms from spring to summer. It often produces fruits known as "pods". Prosopis spp. are able to grow up to 8 m tall, depending on site and climate. It is deciduous and depending on location and rainfall can have either deep or shallow roots. Prosopis is considered long-lived because of the low mortality rate after the dicotyledonous stage and juveniles are also able to survive in conditions with low light and drought. The Cahuilla indigenous people of western North America were known to eat the seeds of mesquite.
Prosopis spp. have been in North America since the Pliocene era and their wood has been dated to 3300 yr BP. They are thought to have evolved with megafauna in the New World. The loss of North American megafauna at the end of the Pleistocene era gave way to one theory of how the Prosopis spp. were able to survive. One theory is that the loss of the megafauna allowed Prosopis spp. to use their fruit pods to attract other organisms to spread their seeds; then, with the introduction of livestock, they were able to spread into grasslands. Another is that Prosopis spp. had always been present in grasslands, but recurring fires had delayed plant and seed development before the emergence of livestock and grazing.
Mesquites grow as a small shrub in shallow soil or as tall as 50 feet (15 m) in deep soil with adequate moisture, and forms a rounded canopy nearly as wide. They may have one or multiple trunks with a multitude of branches. They have bipinnate leaflets of a light green to blue hue that cast a light to deep shade, depending on the species. Spikes of flowers form in spring and summer that form a flat pod of beans 2 to 6 inches (51 to 152 mm) long. Many varieties form thorns. When cut to the ground, the tree can often recover.
Mesquite is native to the US and can be used as a type of lumber. It was a popular type of wood used by early Spaniards to build ships, but is now used most commonly for high-end rustic furniture and cabinets. Scraps and small pieces are used commonly as wood for cooking with smoke in Southern states.
Red-orange sap can be found on the branches of mesquite trees during the summer. This sap was used by those who lived in the desert for several medicinal treatments. The sap was used as a salve and spread on burns and cuts to speed up the healing process. Gargling a mixture of water and sap was used to soothe sore throats, and the same mixture was said to be able to cure upset stomachs. 
Honey mesquite has been introduced to parts of Africa, Asia, and Australia and is considered by the World Conservation Union as one of the world's most problematic invasive species. Its spread into grasslands is mostly attributed to the introduction of domestic livestock, although other factors include climate change, overgrazing, and the reduction of fire frequency. Although Prosopis spp. are naturally occurring in these areas, these changes have resulted in their being able to successfully outcompete other native plants and they are now considered invasive species because they are able to take advantage of vulnerable ecosystems.
Prosopis spp. are different from most invasive species because they are highly invasive in their native and introduced ranges. Their impacts on the invaded ecosystems include changes to hydrological, energy, and nutrient cycling, as well as consequences to biodiversity and primary production.Prosopis spp. density and canopy cover influence the herbaceous layer and native shrubs and are factors in the changes to the ecosystem.
In the United States, Prosopis has become the dominant woody plant on 38,000,000 hectares (94,000,000 acres) of semiarid grasslands. North America is its native range and due to an imbalance within this ecosystem has been able to spread rapidly. It is considered the most common and widely spread "pest" plant in Texas. An estimated 25% of Texas' grasslands are infested and 16 million acres are so invaded that it is suppressing the majority of grass production. In Mexico and the US, the two most problematic species are honey mesquite (Prosopis glandulosa) and velvet mesquite (Prosopis velutina).  Australia is also affected by the introduction of Prosopis spp., in particular, the P. pallida, P. glandulosa, P. velutina, and their hybrid P. juliflora. Prosopis spp. are ranked nationally as one of the 20 most significant weeds. They now cover almost 1 million hectares of land. Prosopis spp. were originally introduced to help with erosion because of their deep root systems. They also have immediate uses to humans through timber and providing a food source through their pods. Since Australia is a hot and semiarid region, Prosopis spp. have been able to become naturalized.
In India, mesquite had been introduced decades ago, but until recently, its effects had not been studied. This genus has been pushing out the Indian wild ass (Equus hemionus khur). This herbivorous mammal eats the pods of Prosopis spp, which was one of the intended purposes of its introduction. Through digesting and excreting the seeds, the Indian wild asses are providing the habitat needed for germination. The 5,000-km2Indian Wild Ass Sanctuary is experiencing mesquite invasion of roughly 1.95 km2 a year. By overtaking the land, the dense canopy cover of mesquite has made it so native vegetation cannot grow. It has also made watering holes inaccessible to the animals within this region. This lack of resources and range is forcing the endangered Indian wild ass into human landscapes and agriculture fields and locals are killing these asses to protect their crops.
Controlling mesquite is a challenging task. One often-used method is mechanical control. This can be effective with high mortality rates if stems are cut at least 20 cm underground. Another method is through the application of herbicides, done on an individual plant basis. Basal application is effective to mesquite of all sizes, while foliar application is best for plants smaller than 1.5 m. Another physical option for control is through fires. Some species of mesquite are fire-sensitive, while others are fire-tolerant. For those that are fire-sensitive, this method can be highly effective, but those that are fire-tolerant require hot and intense fires to be effective. In Australia, scientists are trying biological control methods. They have introduced multiple insects, but the most effective in causing high population level impact is the leaf-tying moth (Evippe spp.). The most recommended method for managing Prosopis, both in native and introduced ranges, is by targeting large numbers of plants either through herbicide or physical removal. Also, research is being done on using satellite and aerial images to assess canopy cover and determine which ranges should be targeted.