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Yucca (Yuca, native name for the manihot or cassava, erroneously applied to the present plants by Gerarde). Liliaceae, tribe Yucceae. Bold stiff-leaved plants suitable for lawn planting, subtropical massing, and a few of them for flower-garden use.
Acaulescent to arboreous endogens with fibrous evergreen sword-shaped lvs. usually pungent and often denticulate or fibrous on the margin: fls. white or shaded with cream or violet, cup- or saucer-shaped, usually pendent in large usually erect panicles, opening at night and then somewhat sickishly fragrant; pollination rarely occurs except through the aid of a small white moth, Pronuba yuccasella, found wherever yuccas occur wild on the continent, which deliberately gathers the pollen and thrusts it into the stigmatic chamber, its larvae feeding exclusively on the maturing seeds of these plants: fr. either capsular and erect or fleshy and hanging in the principal groups or sub-genera.—About 30 species, confined to N. Amer. and the W. Indies, most of them native to the arid S. W. U. S. and the Mexican tableland. A few species have been cult. for centuries, and within the last decade a large number of artificial hybrids have been produced and intro. into cult., especially along the Medit. There are recent monographs by the writer in Rep. Mo. Bot. Card., Vol. 13, pp. 42-116, with illustrations, and by Molon in a small manual "le Yucche," Milano, 1914, in which many of the Sprenger hybrids are also figured. See Hesperoyucca, Samuela.
Propagation is by seeds, offsets, stem-cuttings or rhizome-cuttings. These should be planted in well-drained sandy loam, usually in the succulent house. The only species hardy where frost is severe are Y. glauca, Y. filamentosa, Y. flaccida, Y. baccata, Y. recurvifolia, and Y. gloriosa, which flower in the sequence given, the last-named often blossoming late in autumn. Y. Treculeana shows considerable resistance to frost. The tender species are kept in the cactus house. Well-drained sandy loam suits yuccas best, but with good drainage they are tolerant of a large range of soil and exposure. Y. Treculeana blooms usually in March in plant-houses, as when wild, and the Mexican species when brought to flower are usually spring bloomers, but they often refuse to flower for long periods and then suddenly and unexpectedly produce an abundance of simultaneous bloom, even on the smaller plants. Of the hardy species, Y. glauca flowers in June and it is quickly followed by Y. filamentosa and Y. flaccida, while the forms of Y. gloriosa, which usually flower only at intervals of several years, bloom from late August to so late in the autumn as to be cut down by frost. The only well-known yucca in northern gardens is the common Adam's needle, Y. flaccida. This persists for years, sending up a tall panicle of cream-white flowers in late spring; or early summer. All yuccas are suited to bold and formal effects in gardening; as tub specimens they may be used effectively in subtropical bedding or massing.
Most yuccas may be fertilized if fresh pollen is transferred directly from the anther to the stigmatic cavity of a newly opened flower, preferably one seated directly on the main shaft, where nutrition is more certain. Y. aloifolia commonly fruits freely, but the others rarely fruit spontaneously in cultivation except Y. filamentosa and Y. flaccida, which are pollinated by the small white moth (Pronuba yuccasella) that accompanies them when cultivated in the western states, but emerges from the pupa too late to pollinate Y. glauca and disappears top early for Y. gloriosa. See Rep. Mo. Bot. Gard. 3:99; 4:181, for additional discussion.
The great yuccas, or "yucca palms," of southern California are chiefly Y. arborescens. They grow in the higher lands bordering the Mojave and adjacent deserts, reaching a height of 15 to 20 feet. The old plants are exceedingly weird and picturesque. Occasionally this species is transferred to gardens, but it is apparently not in the trade. This "Joshua tree" is now separated as Clistoyucca arborescens, Trelease; as it is not in cultivation, it need not be discussed further here except to say that Clistoyucca differs from Yucca in its very short style, fleshy incurved perianth, and spongy dry indehiscent fruit.
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