Yucca brevifolia
Joshua Tree

Yucca brevifolia, Red Mountain, Highway 395, Western Mojave Desert

The magnificent Joshua Tree, Yucca brevifolia, is endemic to the Mojave Desert region of the southwestern United States. The earliest known record of Joshua Tree is by J. C. Fremont in 1844, an army lieutenant who became one of the important explorers in the Kern and Tulare Counties regions of California. The Fremont Cottonwood, Populus fremontii, is named in honor of him.

Fremont's Cottonwood, Populus fremontii,
Kern River Audubon Preserve, Hwy 178, Weldon

One version for the origin of the common name "Joshua" is that it was given by Mormons who crossed the Mojave Desert in the 19th century. The shape of the tree and arching branches reminded them of the Biblical character, Joshua, who raised his hands in prayer.

For other versions, see:

How Did the Joshua Tree Get its Name?

The botannical name "Yucca" comes from the Carribean "yuca" which refers to a different plant. The word was adopted by Linneaus as the Yucca genus.

In 1935 Susan McKelvey, botanist at the Arnold Arboretum of Harvard University, described Yucca brevifolia var. jaegeriana which she observed in the Eastern region of the Mojave Desert. This variety is named in honor of Edmund C. Jaeger, naturalist and educator in Riverside, California. It usually branches lower on the trunk than Y. brevifolia and has shorter leaves.

Yucca brevifolia var. jaegeriana,
Living Desert Zoo and Gardens, Palm Desert

In 1959, Philip Munz, botanist, taxonomist and educator at the Rancho Santa Ana Botanic Garden, recognized Yucca brevifolia var. herbertii, which is found mainly in Kern County in the Western Mojave Desert. This variety is named for the botanist, Herbert John Webber. One of its characteristics is a robust spreading root stock (rhizomes) which produce offshoots, observed especially following fires.

Yucca brevifolia var. herbertii, Highway 178, Kern County, Western Mojave Desert.

Taxonomists have argued for other varieties; for raising from variety to sub-species; and even for creating a separate species, Yucca jaegeriana. However, Jepson recognizes just one species with two varieties.



There are two species of Yucca Moths, genus Tegeticula, that pollinate Y. brevifolia. Western Y. brevifolia are primarily pollinated byT. synthetica, while the eastern Y. brevifolia var. jaegeriana are primarily pollinated by T. antithetica.

Trees pollinated by the largerT. synthetica have significantly longer stylar canals. This moth has a longer ovipositor, whereas T. antithetica has a shorter ovipositor for Y. brevifolia var. jaegeriana to accommodate its shorter stylar canal.

[See p. 7 of the Reference below for further description and illustrations.]

Some biologists are concerned about the future of the Joshua Tree. In the Joshua Tree National Park, recent droughts and excessive hot summers have put an undue stress on the trees.

The group, WildEarth Guardians, has petitioned the U.S. Secretary of the Interior to list the Joshua Tree as an endangered species:

"Joshua trees exist in a precarious equilibrium. They have evolved a mutualistic relationship with yucca moths, on which they depend for pollination. They depend for seed dispersal on the vagaries of rodent caching. They require a narrow climate window to thrive. Lastly, Joshua trees are slow-growing, slow-reproducing plants and therefore respond very slowly to changes in their environment.

"The delicate balance allowing Joshua trees to survive is being disrupted by several humancaused threats. Climate change is first among them; climate models indicate that by 2100, as much as 90% of Joshua tree habitat may disappear. Secondary and interacting threats include drought, pollution, invasive plants, and changing fire regimes.

"These iconic trees are an irreplaceable part of the Mojave Desert and the American landscape. Because of their nature, efforts to save them must look to the future on a timescale of decades, if not centuries. We therefore urge the Service to take the long view and proactively conserve these incredible plants before they become endangered."





Yucca brevifolia

Yucca brevifolia var. herbertii

Flora in
Yucca brevifolia habitats

Nature's Recovery

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