I was inspired to write about Yucca brevifolia by two of my friends with whom I went rock-climbing a couple weekends ago in Squamish, British Columbia. The pair of them had just returned from Joshua Tree National Park in southern California. They told me of this interesting species the park is named for, which they happened to see in bloom. Today’s images, though, are courtesy of Damon Tighe@Flickr.
Yucca brevifolia is endemic to the Mojave Desert of southern Nevada, southwestern Utah, southeastern California and western Arizona (it is also sometimes used to define the extent of the Mojave Desert, making it an indicator species as well). Joshua tree survives in low-precipitation areas with hot summers and cold winters (see climate data in the Mojave Desert link). Periods of cold temperatures provide the dormancy thought to prompt flowering in the spring for this tree-like shrub. The flowers bloom from March through May, and are pollinated exclusively by yucca moths in the genus Tegeticula, including Tegeticula synthetica and Tegeticula antithetica. (see: Godsoe W. et al. 2008. Coevolution and Divergence in the Joshua Tree/Yucca Moth Mutualism (PDF). The American Naturalist. 171(6): 826-823).
Joshua tree plants reach 5-20m in height, despite a relatively slow growth rate. The trunk is fibrous with a soft cork-like exterior, and may measure up to 1m in diameter. Older plants are branched and terminate with linear and waxy leaves clustered in rosettes. The egg-shaped flowers of this tree are bunched in panicles, while fruits are indehiscent capsules that become spongy and dry with age.