By the mid 19th century, Mormon migrants had made their way across the Colorado River. Legend has it that these pioneers named the tree after the prophet Joshua, seeing the Joshua tree limbs outstretched in supplication, guiding the travelers westward.

Spring rains may bring clusters of white green flowers on the long stocks at branch tips. Like all desert blooms, Joshua trees depend on just the perfect conditions: well timed rains and for the Joshua tree, a crisp winter freeze. Researchers believe that below freezing temperatures may damage the growing end of a branch and stimulate flowering followed by branching. Some Joshua trees grow straight stalks; these trees have never bloomed, which is why they are branchless. In addition to ideal weather, the pollination of flowers requires a visit from the yucca moth. The moth collects pollen while laying her eggs inside the flower ovary. As seeds develop and mature, the eggs hatch into larvae which feed on the seeds. The tree relies on the moth for pollination and the moth relies on the tree for a few seeds for her young, a happy symbiosis. The Joshua tree is also capable of sprouting from roots and branches. Being able to reproduce vegetatively allows a much quicker recovery after damaging floods or fires which may kill the main tree.