Mojave Yucca

Mojave yucca (or Spanish dagger, Yucca schidigera) is one of two yuccas that are found in the Reserve. Both have spectacular clusters of creamy white flowers. Mojave yucca can be recognized by the clusters of long, sharp leaves that are carried at the end of a thick trunk and by the leaf edges which produce long, curly fibers.

Mojave yucca grows slowly. As one trunk ages, it may bud off one or more smaller plants near the base. These are connected to the original trunk and are part of the same individual, just as branches above ground are part of the same tree. Over time, the newer trunks may also bud off small plants. As the original trunks die and offshoots grow, successive rings of yucca plants are formed. So long as the connections remain, all plants are part of the same individual which may be hundreds, even thousands of years old.

Description ^2,5,41,76

Mojave yucca is an evergreen shrub or small tree, usually less than 16 feet (15 m) tall, with a thick woody trunk that may be sparingly branched. Vegetative reproduction produces small clumps of plants. The upper portion of the trunk is cloaked with dead leaves, the lower portion is often bare with gray-brown, scaly bark. Clusters of long, stiff, dagger-like leaves are produced at the tops of the branches. Leaves are up to 60 inches (150 cm) long, with stringy fibers curling from the margins and spiny tips. Older Mojave yuccas resemble small Joshua Trees.

Spectacular clusters of densely-packed, bell-shaped flowers are produced in or above the terminal leafy clusters. The bisexual flowers are usually 1-2 inches (3-5 cm) long. The sepals and petals are identical (together called tepals); there are six waxy, cream-colored tepals, free or partly fused at the bases. The outer three tepals are often tinged with purple. There is a single greenish-white pistil with a large, superior ovary, inconspicuous style, and three-lobed stigma. (In our plants, the stigma appears as three double lobes.) At the center of the stigma is a depression. There are six stamens; the filaments are fleshy and flattened front to back and curve up around the ovary. Anthers are attached to the filaments at their bases. Pollen is produced in discrete packets of pollen (called pollinia), rather than released as single grains. Mojave yuccas generally bloom from April to May,¹ although we have found blooms as early as late February in the Reserve.³²⁷

The fruits are pendulous green capsules with white flesh. They are usually 2-4 inches (5-11 cm) long and dry to leathery brown in late summer. In shape, the fruit somewhat resembles a green chili pepper. There are six chambers each of which contains many flattened seeds. Seeds are often dispersed by animals feeding on or stashing the fruit.⁵

Classification  

Yucca is a perennial monocot in the agave family (Agavaceae). Monocots are an early offshoot of flowering plants partly characterized by having a single cotyledon (instead of two), by having parallel veins in the leaves (instead of reticulated) and by having flower parts in multiples of three (instead of four or five).¹⁷⁶

The agave family is in a state of flux.⁴¹ At present, the source we follow,² retains the agave family as a separate family. Others place it as a subfamily of the asparagus family (Asparagaceae).^41,143 It has also been considered a subfamily under the lily family (Liliaceae).¹¹

Members of the agave family are often found in dry habitats.⁷⁶ They are characterized by rosettes of stiff, fibrous leaves^11,76 and by a fruit with two or more chambers that becomes dry and splits open at maturity.⁴⁴ Many have large, erect, conspicuous flower clusters.⁴¹

Mojave yucca is one of two yuccas that are found in the Reserve.⁴⁸ Both have spectacular clusters of creamy white flowers. Mojave yucca can be distinguished from chaparral yucca (Hesperoyucca whipplei) by the clusters of long, sharp leaves that are carried at the end of a thick trunk rather than at the base of the plant, and by the leaf edges which produce long, curly fibers.²

Ecology ^57,59

Cross-fertilization occurs when the pollen from one flower successfully fertilizes a flower of the same species on a different plant. The adaptive advantages of cross-fertilization have sometimes led to elaborate modifications of flower structure and pollinator relationships. Among the most unusual is the symbiotic relationship between yuccas and a small group of moths called yucca moths. Both yuccas and the pollinating yucca moths are dependent on each other for reproduction. The precise species of yucca moth differs according to the yucca species, but the relationships are similar.

The yucca moth that pollinates Mojave yucca is Tegeticula yuccasella.⁵ It is a small, pale, nondescript moth that blends easily into the background of a yucca flower. Instead of a long tongue for harvesting nectar, it has short tentacles around the mouth, which helps it gather yucca pollen.

The yucca blossom has a large, six-chambered ovary, and a thick, fleshy stigma. The pollen-receptive area of the stigma is confined to a small, protected sunken area in the center. The female yucca moth visits several yucca flowers, gathering pollen with the help of her tentacles and forming them into a ball that is carried beneath her chin. When enough pollen has been gathered, the moth flies to another plant and finds a fertile flower. She lays one or a few eggs into the depression on the stigma and then plugs the depression with a small ball of pollen, both fertilizing the flower and sealing in her eggs. The developing moth larvae feed upon the developing yucca seeds. Normally, there too few moth larvae to consume all available seeds, so each flower produces the next generation of both flower and moth. The success of this relationship depends on a careful balance between the number of yucca seeds fertilized and the number of moth eggs deposited.

Human Uses  

Mojave yucca “was and remains a useful plant.”⁵ Throughout its range, native Americans used it for food and medicine; the fibers were woven into cord, sandals, bowstrings, baskets, and cloth; the root was used for washing; the seeds were made into necklaces and toys.^5,76

Out local Kumeyaay were no exception. In the words of Delfina Cuero:¹⁶ “The roots are mashed and used for soap. The leaves were used for fibers in many ways. Leaves were split into narrow strips and used to tie houses together, or strips braided to make pottery rests. Leaves were shredded to fibers to make sandals or quick containers which were used and then thrown away. Flower petals were eaten raw when young and tender; they were boiled twice and the water was thrown off when the petals were older. Some people did not eat the flowers, others did. We strung seeds for beads; chopped them for tea, or ground to cook as mush.”

Today Mojave yucca is used as a food additive for farm animals and pets, and as a flavoring and foaming agent in soft drinks. It has been used in folk medicine to reduce inflammation and combat arthritis – applications that are being studied today in pharmaceutical labs.³²⁴

Interesting Facts ^325,326

Mojave yuccas grow slowly. It has been estimated that the height of the trunk increases less than 1 inch (2.5 cm) a year.⁵  As a yucca matures, it may vegetatively produce one or more offshoots near its base. These are connected to the original trunk in the same way as above ground branches are connected; all are part of the same individual, connected to one another through the original trunk. This process may be repeated through the centuries, forming successive rings of newer trunks. The original trunks may die but, so long as the connections among the newer trunks remain, they are a single individual.

In a Nevada desert, one yucca ring is estimated to be several thousand years old, placing it among the oldest plants on earth.