YUCCA, a genus of the family Liliaceae (q.v.), containing about 3o species. The plants occur in greatest frequency in Mexico and the south-west United States, extending also into Central Amer ica, and occurring in such num bers in some places as to form straggling forests. They have a woody Qr fibrous stem, some times short, and in other cases attaining a height of 3o ft. to 4o ft., and branching at the top into a series of forks. The leaves are crowded in tufts at the ends of the stem or branches, and are generally stiff and sword-shaped, with a sharp point, sometimes flaccid and in other cases fibrous at the edges. The numerous flowers are usually white, bell-shaped and pendulous, and are borne in much-branched terminal panicles. The three-celled ovary is surmounted by a short thick style, dividing above into three stigmas, and ripens into a succulent berry in some of the species, and into a dry three-valved capsule in others. The flowers are fertilized entirely through the agency of certain moths. (See POL LINATION and YUCCA-MOTH.) A coarse fibre is obtained by the Mexicans from the stem and foliage, which they utilize for cordage, and in the south-east United States the leaves of some species, under the name "bear grass," are used for seating chairs, etc. The fruits of some species are cooked as food, and the roots of others contain a saponaceous matter used in place of soap.
Some 15 species of Yucca are native to the United States ; of these nine attain the stature of small trees. Among the best known are the Spanish bayonet ( Y. aloifolia), the Spanish dagger ( Y. gloriosa) and the bear-grass or Adam's-needle ( Y. fila
mentosa), of the south Atlantic and Gulf coast, all of which are planted for ornament. Among the most conspicuous are the Joshua tree (Y. brevifolia), sometimes 35 ft. high, and the Mohave yucca ( Y. mohavensia), 8 ft. to 15 ft. high. An almost stemless species ( Y. Whipplei), called mission bells and Quixote-plant, which rears a stout flower-stalk, 12 f t. to 15 ft. high, bearing an immense cluster, 3 ft. to 6 ft. long, of fragrant, creamy-white, drooping bell-shaped flowers, is a strikingly handsome plant of the southern California chaparral (q.v.). The western Spanish bayonet ( Y. baccata), found from New Mexico to California, bears a dark purple edible fruit.
the name given to a genus of moths, Pronuba, the various species of which are each adapted to a separate species of the yucca (q.v.). The moth emerges at the time of opening of the yucca flowers, which frequently remain open only for a single night. The female moth rolls together a ball of pollen, flies to another flower, lays four or five eggs in the pistil and inserts the pollen mass in the opening thus formed. Each larva, on hatching from the egg, requires about 20 seeds of the yucca plant as food. As the plant produces some 200 ovules, this leaves about ioo seeds over to perpetuate the plant. The yucca can be fertilized by no other insect. The larva of the yucca-moth can only live on its own species of yucca.