Strombocarpa pubescens

Hughes et al. (2022) found that the genus Prosopis is polyphyletic and resurrect segregate genera; Prosopis pubescens is treated as Strombocarpa pubescens.

Prosopis pubescens is a small tree that forms dense woodlands along riparian areas in the southwestern United States. It is the dominant species within mesquite bosques along river corridors and provides food and shelter for many wildlife species. Despite a large range and number of occurrences, this species has experienced catastrophic declines in many populations in the western part of its range due to combinations of factors that are not entirely understood. Heat, drought, flooding, and fungal pathogens likely contribute to these mass die-offs. Additionally, the species is threatened by human disturbance such as water diversions and dams, urban and agricultural development, and livestock grazing.

The native range of Prosopis pubescens extends from southeastern California west into southern Nevada, extreme southwestern Utah, southern and western Arizona, southwestern and south-central New Mexico, western Texas and northern Mexico, including Baja California, Sonora, Chihuahua, and Coahuila. Prosopis pubescens has been introduced to areas in India, Pakistan, and southern and southwestern Africa (Meyer 2005). Range extent was estimated using herbarium specimens, photo-based observations, and NatureServe Network occurrence data collected between 1994 and 2025 (RARECAT 2024, GBIF 2025, iNaturalist 2025, NatureServe 2025, SEINet 2025).

By applying a 1 km separation distance, or 10 km separation distance between occurrences along the same waterway, to herbarium specimens, photo-based observations, and NatureServe Network occurrence data documented between 1994 and 2025, it is estimated that there are more than 300 occurrences rangewide (RARECAT 2024, GBIF 2025, iNaturalist 2025, NatureServe 2025, SEINet 2025).

Prosopis pubescens is dependent on shallow groundwater in desert riparian areas, a habitat affected heavily by humans in the past hundred years (Foldi 2014). Threats to this species include urban and agricultural development, groundwater extraction, surface water diversion and impoundment, livestock grazing, herbicide use, pathogenic canker fungus, and climate change (Foldi 2014, Miller 2018, Cowan 2024).

Examinations of large-scale die-offs have shown that drought followed by flooding has been responsible for some tree deaths at Ash Meadows (DRI 2023). Similar hydrological cycles in reservoirs may kill trees that grow along the edges of the impounded water. Another study has shown the canker fungus Neoscytalidium dimidiatum to be strongly linked to tree deaths in Nevada and likely in Arizona. The wood-boring beetle Chrysobothris octocola was also observed on the infected trees, but it is unknown whether the beetle is a vector or simply attacking weakened trees. The authors speculate that this may be a new strain of a native fungus that developed in the Lower Colorado River area and spread to other populations. The fungus is most active during hot weather and hotter summer temperatures may be contributing to the virulence and spread of the fungus (Cowan 2024).