Yucca brevifolia
| Joshua tree | |
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| Species: | Y. brevifolia
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| Yucca brevifolia | |
The Joshua tree (Yucca brevifolia) is a monocotyledonous tree native to southwestern North America, in the states of California, Arizona, Utah and Nevada. Confined mostly to the Mojave Desert between 400-1,800 m (2,000-6,000 feet), they thrive in the open grasslands of Queen Valley and Lost Horse Valley in Joshua Tree National Park.
Growth and development
Joshua trees can grow from seed or from an underground rhizome of another Joshua tree. They are slow growers; new seedlings may reach a height of 10-20 cm in their first few years, then only grow about 10 cm per year thereafter. The trunk of a Joshua tree is made of thousands of small fibers and lacks annual growth rings, making it difficult to determine the tree's age. This tree is not very sturdy because of its shallow root area and top-heavy branch system, but if it survives the rigors of the desert it can live hundreds of years of age, some up to a thousand years. The tallest trees reach about 15 m tall.
The 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 serrate.
The flowers are produced in spring 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 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 is dependent on rainfall at the proper time. They also need a winter freeze before they will bloom.
Once they bloom, the trees are pollinated by the yucca moth, which spreads pollen while laying her eggs inside the flower. The moth larvae feed on the seeds of the tree, but enough seeds are left behind to produce more trees. The Joshua tree is also able to actively abort ovaries in which too many eggs have been laid.
Ethnobotany
The Cahuilla Native Americans who have lived in the southwestern United States for generations still identify with 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 nutritious meals.
The name Joshua tree was given by a group of Mormon settlers who crossed the Mojave Desert in the mid-19th century. The tree's unique shape reminded them of a Biblical story in which Joshua reaches his hands up to the sky to stop the sun by God's command. Ranchers and miners who were contemporary with the LDS immigrants also took advantage of the Y. brevifolia using the trunks and branches as fencing and for fuel for ore-processing steam engines.
Arizona Joshua tree
Northwestern and western Arizona has areas of Joshua Tree forests, especially from the area around Wickenburg, Arizona northwestwards to the southeastern Lake Mead region. The U.S. route from Wickenburg to Kingman, Arizona is named for the tree, the Arizona Joshua Parkway.
Conservation status
There is some concern[1] from modeling that Joshua trees will be eliminated from Joshua Tree National Park due to climate change, and that this will damage the ecosystem of the park. There is also concern about the ability of the trees to migrate to favorable climates due to the extinction of the giant ground sloth 13,000 years ago.
See also
Gallery
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panicle -
fruit
References
