Creosote (Larrea tridentata)

Creosote (Larrea tridentata)

Larrea tridentata is known as creosote bush and greasewood as a plant, chaparral as a medicinal herb, and as “gobernadora” in Mexico, Spanish for “governess,” due to its ability to secure more water by inhibiting the growth of nearby plants. In Sonora, it is more commonly called “hediondilla.”

It is a flowering plant in the family Zygophyllaceae. The species is named after Juan Antonio Hernandez de Larrea, a Spanish clergyman.

Larrea tridentata is a prominent species in the Mojave, Sonoran, and Chihuahuan Deserts of western North America, and its range includes those and other regions in portions of southeastern California, Arizona, Nevada, southern Utah, New Mexico and Texas in the United States, and northern Chihuahua and Sonora in Mexico. The species grows as far east as Zapata County, Texas, along the Rio Grande southeast of Laredo near the 99th meridian west.

Larrea tridentata is an evergreen shrub growing to 1 to 3 metres (3.3 to 9.8 ft) tall, rarely 4 metres (13 ft). The stems of the plant bear resinous, dark green leaves with two opposite lanceolate leaflets joined at the base, with a deciduous awn between them, each leaflet 7 to 18 millimetres (0.28 to 0.71 in) long and 4 to 8.5 millimetres (0.16 to 0.33 in) broad. The flowers are up to 25 millimetres (0.98 in) in diameter, with five yellow petals. Galls may form by the activity of the creosote gall midge. The whole plant exhibits a characteristic odor of creosote, from which the common name derives.

Creosote bush is most common on the well-drained soils of alluvial fans and flats. In parts of its range, it may cover large areas in practically pure stands, though it usually occurs in association with Ambrosia dumosa (burro bush or bur-sage). Co-evolution in this common habitat is likely responsible for chemicals found in creosote bush roots that inhibit the growth of burro bush roots, but as of 2013 much of their relationship remains unexplained.

Creosote bush stands tend to resemble man-made orchards in the even placement of plants. Originally, it was assumed that the plant produced a water-soluble inhibitor that prevented the growth of other bushes near mature, healthy bushes. Now, however, it has been shown that the root systems of mature creosote plants are simply so efficient at absorbing water that fallen seeds nearby cannot accumulate enough water to germinate, effectively creating dead zones around every plant. It also seems that all plants within a stand grow at approximately the same rate, and that the creosote bush is a very long-living plant.

About the author

Jim Mattern

Jim is a scapegoat for the NPS, an author, adventurer, photographer, radio personality, guide, and location scout. His interests lie in Native American and cultural sites, ghost towns, mines, and natural wonders in the American Deserts.