Yucca brevifolia
Joshua Tree
Family: Asparagaceae
This arborescent (tree-like) yucca is the most iconic plant native to the Mojave desert of northwest Arizona, eastern California, and Nevada. Plants start out with single trunks, but will form multiheaded clusters as they age. Plants can live to be hundreds of years old and can eventually reach a size of 50 feet tall, most specimens will top out around 30 feet. The leaves are dark green to bluegreen, stiff with a serrated edge and terminal spine. Crowns of greenish white flowers occur in spring. The semi-fleshy fruit that is produced is green-brown, elliptical, and contains many flat seeds. Joshua trees usually do not branch until after they bloom (though branching may also occur if the growing tip is destroyed by the yucca-boring weevil), and they do not bloom every year. Like most desert plants, their blooming depends on rainfall at the proper time. They also need a winter freeze before they bloom.
There are two varieties of this species:
Yucca brevifolia var. brevifolia, Joshua tree: arborescent with a distinct trunk and, usually, stout branches. Tends to occur more westerly in the range of the species.
Yucca brevifolia var. jaegeriana, Jaeger's Joshua Tree: generically referred to as dwarf Joshua tree, it tends to branch much lower than the regular Joshua tree. This variety represents the more easterly populations of the species.
The name "Joshua tree" is commonly said to have been given by a group of Mormon settlers crossing the Mojave Desert in the mid-19th century: The tree's role in guiding them through the desert combined with its unique shape reminded them of a biblical story in which Joshua keeps his hands reached out for an extended period of time to enable the Israelites in their conquest of Canaan (Joshua 8:18–26). Further, the shaggy leaves may have provided the appearance of a beard. However, no direct or contemporary attestation of this origin exists, and the name Joshua tree is not recorded until after Mormon contact; moreover, the physical appearance of the Joshua tree more closely resembles a similar story told of Moses.
Photo of Yucca brevifolia var. brevifolia by Jonathan Frank, iNaturalist
Plant in full to part sun in very well-drained soil. Low water when established. Hardy to -10°F.
Though many insects visit the nectar-rich flowers, they are pollinated by a single species of moth. The yucca moth, Tegeticula synthetica, is commonly considered Joshua tree's pollinator. Researchers have discovered another Joshua tree pollinator, Tegeticula antithetica, in the eastern and northeastern parts of the Mojave Desert where Y. b. var. jaegeriana occurs. Distributions of the 2 moth species are not thought to overlap. It is generally accepted that a female moth emerges from her pupa near a Joshua tree plant, mates in a flower, and flies to a freshly opened flower. Using specialized mouth parts sometimes referred to as "tentacles," she scrapes pollen from the anthers, forms it into a ball, and carries it between her tentacles and thorax to another flower. Whether or not the receiving flower is on the same inflorescence or tree is often speculated, but direct observation is lacking. The female moth penetrates the ovary wall and deposits 1 or more eggs in a locule. All eggs may be put in 1 locule or eggs may be distributed among several locules. She then pushes the pollen ball into the stigmatic tube. Moth larvae feed on the developing Joshua tree seeds.
Joshua trees are also important nesting and perching sites for birds. Red-shafted flickers make nests in the branches, which are later used by other birds.
Several parts of the Joshua tree are used as food and fiber. Leaf fibers are occasionally used to bind and manufacture sandals. Root sheaths are woven into baskets to add reddish-brown designs. Fruits are baked or boiled then eaten. Seeds are ground into flour and mixed with flour from other plant species. The flour is moistened with water and the resulting paste is kneaded into cakes and dried.
There is confusion between the word yuca and yucca and this goes back to the father of botany: early reports of the species were confused with the cassava (Manihot esculenta). Consequently, Linnaeus mistakenly derived the generic name for Yucca from the Taíno word for the cassava, yuca. The species, brevifolia, means short leaf. The variety jaegeriana was named for Edmund C. Jaeger, an American biologist known for his works on desert ecology.
The Joshua tree is native to the southwestern United States (Arizona, California, Nevada, and Utah) and northwestern Mexico. This range mostly coincides with the geographical reach of the Mojave Desert, where it is considered one of the major indicator species for the desert. It occurs at elevations between 1,300 and 5,900 ft.
Photo of Yucca brevifolia var jaegeriana by appleberry, iNaturalist
Flowers of Yucca brevifolia var. jaegeriana. Photo by Jim Boone, iNaturalist
Fruits of Yucca brevifolia var. brevifolia. Photo by Russell V. Di Fiori, iNaturalist.
Remains of a dead joshua tree, photo by psiloveyou on iNaturalist