Yucca brevifolia


Yucca brevifolia is a plant species belonging to the genus Yucca. It is tree-like in habit, which is reflected in its common names: Joshua tree, yucca palm, tree yucca, and palm tree yucca.
This monocotyledonous tree is native to the arid southwestern United States, specifically California, Arizona, Utah, and Nevada, and to northwestern Mexico. It is confined mostly to the Mojave Desert between elevation. It thrives in the open grasslands of Queen Valley and Lost Horse Valley in Joshua Tree National Park. A dense Joshua tree forest also exists on the Cima Dome in the Mojave National Preserve; northeast of Kingman, Arizona, in Mohave County; as well as along U.S. 93 between the towns of Wickenburg and Wikieup, and designated as the Joshua Tree Parkway of Arizona. The Joshua Tree has barely any leaves, just a few balls on the edges.
The Joshua tree can appear in the Mojave desert most of the time. It rarely appears in Death Valley.

Taxonomy

The Joshua tree is also called izote de desierto. It was first formally described in the botanical literature as Yucca brevifolia by George Engelmann in 1871 as part of the Geological Exploration of the 100th meridian.
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 guide the Israelites in their conquest of Canaan. 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.
Ranchers and miners who were contemporary with the Mormon immigrants used the trunks and branches as fencing and for fuel for ore-processing steam engines. They referred to these fallen or collapsed Joshua trees as tevis stumps.
In addition to the autonymic subspecies Yucca brevifolia subsp. brevifolia, two other subspecies have been described: Y. b. subsp. jaegeriana and Y. b. subsp. herbertii, though both are sometimes treated as varieties or forms.

Growth and development

Joshua trees are fast growers for the desert; new seedlings may grow at an average rate of per year in their first 10 years, then only about per year. The trunk consists of thousands of small fibers and lacks annual growth rings, making determining the tree's age difficult. This tree has a top-heavy branch system, but also what has been described as a "deep and extensive" root system, with roots reaching down to. If it survives the rigors of the desert, it can live for hundreds of years; some specimens survive a thousand years. The tallest trees reach about. New plants can grow from seed, but in some populations, new stems grow from underground rhizomes that spread out around the parent tree.
The evergreen leaves are dark green, linear, bayonet-shaped, 15–35 cm long and 7–15 mm broad at the base, tapering to a sharp point; they are borne in a dense spiral arrangement at the apex of the stems. The leaf margins are white and serrated.
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Flowers typically appear from February to late April, in panicles 30–55 cm tall and 30–38 cm broad, the individual flowers erect, 4–7 cm tall, with six creamy white to green tepals. The tepals are lanceolate and are fused to the middle. The fused pistils are 3 cm tall and the stigma cavity is surrounded by lobes. The semifleshy fruit that is produced is green-brown, elliptical, and contains many flat seeds. Joshua trees usually do not branch until after they bloom, 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.
Once they bloom, the flowers are pollinated by the yucca moth, which spreads pollen while laying eggs inside the flower. The larvae feed on the seeds, but enough seeds remain to reproduce. The Joshua tree is also able to actively abort ovaries in which too many eggs have been laid.

Distribution and habitat

Y. brevifolia is native to the Southwestern United States with populations in western Arizona, southeastern California, southern Nevada, and southwestern Utah, and to 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 altitudes between.

Conservation status

Joshua trees are one of the species predicted to have their range reduced and shifted by climate change. Concern remains that they will be eliminated from Joshua Tree National Park, with ecological research suggesting a high probability that their populations will be reduced by 90% of their current range by the end of the 21st century,thus fundamentally transforming the ecosystem of the park. Also, concern exists about the ability of the species to migrate to favorable climates due to the extinction of the giant Shasta ground sloth 13,000 years ago; ground sloth dung has been found to contain Joshua tree leaves, fruits, and seeds, suggesting that the sloths might have been key to the trees' dispersal.

Uses and cultivation

Different forms of the species are cultivated, including smaller plants native from the eastern part of the species range. These smaller plants grow 2.5 m tall and branch when about 1 m tall. Red-shafted flickers make nests in the branches, which are later used by other birds.
Cahuilla Native Americans, who have lived in the Southwestern United States for generations, identify this plant as a valuable resource and call it hunuvat chiy’a or humwichawa. Their ancestors used the leaves of Y. brevifolia to weave sandals and baskets, in addition to harvesting the seeds and flower buds for meals. Native Americans also used the reddish roots to make dye. Yucca tree roots have saponin glycosides.