Joshua tree

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For the album by U2, see The Joshua Tree. For the census-designated place in California, see Joshua Tree, California.

{{Taxobox | color = lightgreen | name = Joshua tree | image = jtree.jpg | image_width = 240px | regnum = Plantae | divisio = Magnoliophyta | classis = Liliopsida | ordo = Asparagales | familia = Agavaceae | genus = Yucca | species = Y. brevifolia | binomial = Yucca brevifolia | binomial_authority = Schott ex Torr. }}

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.

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 a couple hundred years. The tallest trees reach about 15 m tall.

The leaves are 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 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 tepals. Joshua trees usually do not branch until after they bloom (though branching may also occur if the growing tip is detroyed by the yucca-boring weevil), and they don't 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 name Joshua tree was given by a band of Mormons 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.