Looking like one of Dr. Seuss' creations, the Joshua tree stretches it's spiky-crowned arms toward the desert skies above the American Southwest. Early Mormon settlers gave the plant its name, because it reminded them of the Biblical Joshua, pointing the way to the Promised Land. In fact, however, the Joshua "tree" isn't a tree at all; it's the world's largest yucca plant, Yucca brevifolia, a member of the sturdy desert-dwelling branch of the lily family. Ranging across parts of California, Utah, Arizona, and Nevada, the Joshua tree is a dry-land specialist. Most live in the Mojave Desert, though some can also be found in the Sonoran. Joshua trees grow best on flat or slightly sloping ground, at altitudes of 2,000 to 6,000 feet. Joshua trees grow very slowly in their harsh environment, less than one inch per year after their sapling stage. The plants can live for hundreds of years, though, so the tallest are more than 40 feet high! Joshua trees generally have one main trunk covered with shaggy "bark," supporting a number of arms topped with dagger-shaped leaves. Unlike true trees, Joshua tree trunks are comprised of bundled fibers, rather than concentric annual growth rings. The giant yucca have surprisingly shallow root systems, which spread out near the surface rather than reaching down into the ground. This adaptation allows the Joshua tree to take advantage of any rain that hits the desert floor, but it also leaves the plant vulnerable to blowing over during storms.