Yuccas (Yucca) are iconic perennials, found across a wide geographic area, stretching from Canada to South America. The fifty-odd species that comprise the genus inhabit a variety of different climate zones across this range, but most are native to arid habitats.
Because they provide the raw materials necessary for making many basic necessities, yuccas have been important to people for hundreds of years; while they are not commercially important in the modern world, several species are very popular, drought-tolerant ornamentals.
Most yuccas possess a few key traits that characterize the entire genus. These include the presence of long, pointed leaves that arise from a dense rosette, and tall, “floating” inflorescences. Some forms remain close to the ground and superficially resemble a tuft of giant grass, while others (especially some of the most famous members of the group) produce a tree-like growth form.
Taken as a whole, the genus Yucca displays a diverse array of adaptations that help them survive in arid habitats. Many of these traits make these plants particularly well suited for ornamental use in Southern California. Yucca plants thrive best in full sun exposure, but they can thrive in most well drained soils, and require very little (if any) supplemental irrigation once established.
Most of the species possess thick leaves and many feature a thick wax layer on the surface of the leaves; both adaptations help slow the rate of transpiration, and therefore, reduce the amount of water the plants lose. Some species shed their leaves and become dormant during dry, hot summers. In doing so, the plants typically shed their leaves to halt transpiration altogether. Additionally, the shed leaves provide some protection against the sun’s harsh rays.
While a few yuccas are capable of self-pollination, most require crosspollination to produce seeds. Accordingly, most yucca species relies on insects – specifically, a group of lepidopterans called yucca moths – for pollination.
While feeding on the nectar produced by yucca flowers, the moths ferry pollen from male flowers to females, thus ensuring crosspollination. Because yucca moths also deposit their eggs on the female flowers, the hatching larvae enjoy a ready food source: the developing seeds.
Several yucca species are particularly interesting. Some of the most notable species include:
Joshua trees (Yucca brevifolia) are often mistaken for true trees, as they produce tall, thick trunks that branch in multiple locations. Found throughout the Mojave Desert, Joshua trees actually serve as an indicator species for the Mojave community. Joshua trees were important to the Cahuilla people (historic inhabitants of the Mojave region), who used the tough leaves of the plants to make sandals and other durable goods, and collected the flower buds and seeds as a food source.
Like Joshua trees, soaptree yuccas (Yucca elata) are native to the American southwest, but they inhabit the Sonoran and Chihuahua Deserts, rather than the Mojave. Also like Joshua trees, soaptrees provided a variety of resources for Native Americans living alongside them. In addition to stiff plant fibers used to produce baskets, sandals, cordage and similar items, a soapy substance found within the plant’s trunk and roots was harvested for use as a soap or shampoo.
Spineless yuccas (Yucca elephantipes) are quite tree-like, and they often produce several different “trunks.” Perhaps unsurprisingly, the spineless yucca is the tallest member of the genus Yucca, and it occasionally reaches 30 feet in height.
Spineless yuccas are popular ornamentals in many warm regions, including not only California and Arizona, but also the relatively humid south Florida region. Unlike many other yuccas, including the aptly named needle-palm (Yucca filamentosa) and Spanish dagger (Yucca gloriosa), which possess stiff terminal spines that probably serve to discourage predators; spineless yuccas lack hazardous terminal spines.
Thanks to their striking pale blue leaves, beaked yuccas (Yucca rostrata) are popular ornamentals. These yuccas also grow like small trees, and often reach heights of 15 feet or more.