Yucca brevifolia – “Joshua Tree”

Also Known As: Tree Yucca, Yucca Palm, Palm Tree Yucca, Izote de Desierto (Desert Dagger); Cahuilla names: Hunuvat chiy’a, Humwichawa
Family: Agavaceae (Century Plant Family)
Bloom Period: Mar-Jun
Form: Large, multi-branched evergreen shrub or tree
Habitat: Throughout the Mojave desert at elevations between 2000 and 6000 feet (600-1800 m)
Leaves: Linear and pointy, like daggers, margins smooth
Translation: “Yucca” is from the Carib name for the cassava, a root vegetable, so its use here is a misapplication that stuck; “brevifolia” is Latin for “short-leaved,” since its leaves are short for a Yucca.
Notes: Common name given by Mormon settlers referring to a character in their mythology who famously raised his arms skyward in prayer. Can grow to be 49 feet (15 m) tall – 20-30 feet (9-13 m) being average – with root systems that extend 36 feet (11 m) away from the base. Age is difficult to determine because it lacks growth rings like other trees, but estimates based on other means point to potential lifespans measured in the hundreds of years. Does not flower every year. Can also reproduce by sending up shoots from underground runners, which accounts for the clutch of younger plants sometimes seen around older ones. Close-up of flower shown bottom left. Fruit shown bottom right.
Native American Uses: The Cahuilla ate the flowers, the Tübatulabal the immature pods, and the Kawaiisu the pits of the fruit, which they roasted, mashed, dried and stored. An alcoholic drink was brewed from the seeds. The Cahuilla made sandals and nets from the fibers. The Kawaiisu, Shoshone and Timbisha used the red inner roots in basket-making. Other Southwest Native Americans made the tree’s fibers into cordage and used it as a base for fur garments.
Animal Associations: The Joshua Tree is central to its ecosystem and plays roles for many desert animals. It is a nesting location for at least 25 species of birds and owls, hunting grounds and shelter for lizards, a high vantage point for ground squirrels, a source of housing material for the Desert Woodrat, and home and mating territory for dozens of species of insects. Fruits are eaten by the White-Tailed Antelope Ground Squirrel and the Mojave Ground Squirrel, who will both climb up to the tops of the trees to harvest them. (Sitting outside near a group of Joshua Trees one day, I was startled but amused when a ground squirrel knocked a fruit out of a tree nearby!) The trunk is a favorite drilling site for the Ladder-Backed Woodpecker. Fallen branches and trunks provide critical habitat for the Desert Night Lizard, which waits out the hot days in their shade. New shoots are larval food of the Colorado Yucca Borer butterfly. In the Pleistocene Era, over 10,000 years ago, the seeds might have been dispersed in part by the Shasta Ground Sloth; they have been found in the sloth’s ancient dung heaps in dry caves.

In a classic case of what biologists call a “mutualistic relationship,” the flowers are pollinated exclusively by two species of Yucca Moth and the diet of their larvae is comprised entirely of the Joshua Tree’s developing seeds. When it is egg-laying time, the female moth uses tentacle-like mouth parts to collects pollen, which she forms into a clump and stores in hairs under her chin. (She is specially equipped with these parts instead of the tongue-like proboscis that moths and butterflies typically have.) She then flies to a different flower on a different tree (which ensures genetic diversity) and – using olfactory organs on her antennae – checks by smell to see if the flower has already been pollinated by another moth. Too many eggs in one flower will cause the ovary to abort its seeds, starving the moth larvae. If the flower still has vacancy, she pierces the base of the flower’s ovary with her sharply pointed ovipositor (“egg-placer”) and lays eggs inside one of the ovary’s six chambers. Last, she takes some of the pollen from under her chin and places it on the end of the stigma, the flower’s female part that tops the ovary. In this way, the flower is pollinated and when the larvae hatch, they will have food on-hand in the form of the developing seeds. Generally, the larvae don’t eat all the seeds, leaving behind enough for new plants. I don’t believe in Creationism, but I personally find it difficult to imagine how such a complex (and frankly wondrous) relationship is the result of random mutations.