When Mormon settlers crossed the Mojave in the mid-19th century they "saw" the hands of Joshua reaching towards the heavens... so goes the origin of this tree's colloquial name. Joshua Trees (Yucca brevifolia) are a tree-like monocot plant that belong to the family Agavaceae. Although they are not true trees that produce growth rings with a woody core, this top heavy plant stretches nearly eleven meters towards the desert sky. The asymmetric branching and long spiky leaves remind me of the lonely acacias that dot vast stretches of the African savanna. Restricted to an altitude of 400 to 1800 meters, Joshua trees are an icon of the high desert. Their survival is contingent on adapting to the arid environment, and the plant's morphology reflects its evolution. A long taproot that seeks deep pockets of water, waxy leaves that prevent desiccation, and reproduction timed to ephemeral rains are an adaptive response to life in the desert. Following a heavy precipitation event, large clusters of fragrant white flowers (panicles) emerge and await their pollination. The pollinator is an obligate symbiont known as the pronuda yucca moth. Female moths will deposit eggs into the panicle and, in doing so, cross pollinate the trees. Larval moths feed on developing seeds and will emerge following metamorphosis. The yucca moth and Joshua tree coexist in a mutualistic relationship in which both the moth and tree benefit from their codependency.

* Did You Know #37 is a modification of a blog that I first posted on April 9, 2011