Larrea is a genus of five species of evergreen shrubs in the family Zygophyllaceae (caltrop family), placed in the order Zygophyllales. The genus is native to the Americas, with species distributed across arid and semi-arid regions of South America and the deserts of North America. South American members — known collectively as jarillas — are closely related and can produce fertile interspecific hybrids.
The shrubs are evergreen and typically grow to 1–3 metres in height. Leaves are small and resinous, composed of two opposite lanceolate leaflets joined at the base. Flowers have five yellow petals, and the fruit is a small, fuzzy spherical capsule that splits into five one-seeded carpels at maturity. The foliage is coated in resin and produces a distinctive creosote-like odour that intensifies after rain — in desert regions the scent is widely associated with rainfall.
The most well-known member is the creosote bush (Larrea tridentata), dominant across the Mojave, Sonoran, and Chihuahuan Deserts of southwestern North America. It is one of the most drought-adapted plants on Earth, forming vast near-pure stands across alluvial flats; its root systems absorb water so efficiently that they create effective dead zones preventing competitors from establishing nearby. A clonal colony of creosote bush in the Mojave Desert — known as King Clone — is estimated to be approximately 11,700 years old, making it one of the oldest living organisms on Earth.
The genus was named in honour of Bishop Juan Antonio Hernández Pérez de Larrea, an 18th-century Spanish patron of science.
Etymology
The genus name Larrea honours Bishop Juan Antonio Hernández Pérez de Larrea, an 18th-century Spanish bishop and patron of science. The common name "creosote bush" for L. tridentata derives from the characteristic tar-like odour of the plant's resinous leaves, which resembles that of creosote.
Distribution
Larrea species are native to the Americas, occupying arid and semi-arid zones across two major geographic regions. South American species (L. cuneifolia, L. divaricata, L. nitida) are distributed across the Monte and Patagonian deserts of Argentina. Larrea tridentata dominates the Mojave, Sonoran, and Chihuahuan Deserts of the southwestern United States (California, Arizona, Nevada, Utah, New Mexico, Texas) and northwestern Mexico (Chihuahua, Sonora, Coahuila, and adjacent states).
Ecology
Creosote bush (L. tridentata) is emblematic of North American hot desert ecology. It grows predominantly on well-drained alluvial fans and flats, where it often forms near-pure stands with remarkably even plant spacing. This spacing arises not from allelopathic chemicals, as originally hypothesised, but because the extensive root systems of established plants absorb soil moisture so completely that seeds falling nearby cannot accumulate sufficient water to germinate. The species is associated with Ambrosia dumosa (burro bush), and root exudates from creosote bush inhibit burro bush root growth. The shrubs support a specialist community including desert iguanas, chuckwallas, jackrabbits, desert woodrats, kangaroo rats, and at least 22 bee species that rely on the flowers for pollen and nectar.
Cultural Uses
Several Native American peoples of the American Southwest used Larrea tridentata extensively. The Coahuilla treated intestinal complaints and tuberculosis with it; the Pima used leaf decoctions as an emetic and boiled-leaf poultices on wounds; the Tohono O'odham applied it for stiff limbs, snakebite, and menstrual cramps, and also boiled the plant's reddish lac to produce a glue for repairing broken pottery. The plant (sold under the name "chaparral" as a herbal supplement) remains widely used in traditional medicine in Mexico, though both the US FDA and Health Canada have issued warnings against internal use due to documented risk of liver and kidney damage.
