Yucca brevifolia (Agavaceae).

This tree — the Joshua tree, to use its common name — has the Mojave desert — in the states of Arizona, Utah, California, Nevada— as its habitat: at elevations ranging between 600 and 1 800 m (2 000-6 000 ft). It towers over a shrub canopy that usually also includes sagebrush, blackbrush, Mojave yucca, buckwheat and creosote bushes.
The Joshua tree somewhat resembles a genealogical tree, with branches springing perpendicularly to the trunk and to one another. There are no tree rings, but a spongy pulp material instead. The plant grows from a seed or from a rhyzome of an earlier existing tree. The growth rate is astonishingly slow, 10-20 cm (4-8 in) the first year, only 10 cm (4 in) in subsequent years. It can live up to three centuries. 
It is only after the plant has grown 25-30 cm (10-12 in) that it develops its narrow, sword-shaped pointed leaves. As for the flowers, the tree has to reach 2-3 m  (8-10 ft) before it starts to produce them. In early spring, the stalk is covered with green pods, with 7-9 buds in grouped clusters on each new branchlet. 
Inflorescences appear once or twice every year, rarely on the same branch. The white flowers, usually visible from the end of February until April, have partially opened petals. Flowering depends on earlier rainfall and on a cold winter. 
Yucca brevifolia is remarkable for its symbiotic relationship with its pollinator, a tiny white moth, Pronuba tegeticula synthetica. The moth collects the sticky pollen, gathers it into a ball that it deposits, together with its own eggs, into the pistil.
On a souvent besoin d’un plus petit que soi, according to La Fontaine, a French seventeenth-century writer : ‟one often needs someone smaller than oneself.‟ The smaller entity can make you live and be prosperous, as is the case with the Joshua tree — or with the microbiome in our guts. It can also kill you, as with pathogenic bacteria. Or, among plants, Ponderosa pines infested and killed by Dendroctonus ponderosae, a beetle whose larvae devastate those incredibly handsome trees — a blight currently affectng them along the entire ranges of the Sierras and the Rocky mountains, from Canada to Southern Colorado and California.
Why the name Joshua tree? It was thus named, allegedly, by Mormons during the nineteenth century. The name, Joshua tree, is out of the Bible. The biblical reference is very American: for two main reasons, the religiosity of the people; their anti-elitist distrust of a high-brow education, in the European style, high on Greek and Roman antiquity. Hence, to Americans — to Europeans much less — the Bible is both a sacred and a standard reference book. The name of the Joshua tree, together with the swearing-in procedure at a trial, Congress committee hearing, or with a new President, is a reminder.