CELASTRALES

order of flowering plants, belonging to the class Magnoliopsida, or the dicotyledons (q.v.; characterized by two seed leaves). Its members are chiefly trees belonging to 12 families, 147 genera, and about 2,000 species. Four of the familiesthe Aquifoliaceae (holly), Celastraceae (staff-tree), Icacinaceae (icacina), and Hippocrateaceae (hippocratea)are broadly distributed in the world and contain about 90 percent of the species. They are components of forests, requiring moderately rich soil. Many of the 300 species of the holly family (Aquifoliaceae) are native in the tropics of Central and South America and the warmer regions of Asia. Several well-known hollies, however, range northward into southern Europe and the eastern United States. Ilex aquifolium, the European holly, grows 50 feet (16 m) tall and furnishes valuable wood for veneers. It is used for decoration, and hundreds of horticultural varieties are available for ornamental plantings. The American holly (I. opaca) is widely distributed in the warmer areas of the eastern United States and is grown in commercial orchards for its red, yellow, or black berrylike fruits. Wood of this species is valuable in cabinetmaking and interior finishing. I. opaca, with more than 1,000 horticultural varieties, is also used as an accent tree, for street plantings, wind barriers, and even bonsai. The dried leaves of I. paraguariensis are used in South America to prepare a caffeine-rich beverage, yerba mat. Of the 55 genera in the staff-tree family (Celastraceae), Celastrus and Euonymus are best known in the Northern Hemisphere. Celastrus scandens, the American bittersweet, is a shrub that can twine on a trellis or overrun a wooded area by climbing into tall trees. In autumn its dry capsules open to reveal bright orange clumps of berrylike arils that are often used for their colour in dry bouquets. Many of the Asiatic species and cultivars of Euonymus are evergreen. E. fortunei, native to central and western China, has yielded many types of ground covers, hardy as far north as New England. Cultivars of the European spindle tree (E. europaea) attain heights of 20 feet (6 m) and display arils ranging in colour from orange to lavender-pink. The Icacinaceae family is composed of tropical trees and vines with its major centre of distribution in the Southern Hemisphere. A few species of its 58 genera (and 400 species), such as Pennantia and Villarsia, are cultivated locally as ornamentals. Members of the Hippocrateaceae, a family of woody vines and slender trees, are native chiefly to South America but are also found in Africa. Latex ducts, producing a milky sap, occur in many members. In Celastrus and Euonymus a unique, asexual method of reproduction has evolved. In addition to the embryo that is formed by fertilization of the egg within the ovule, another embryo may arise from the inner seed-coat area. Thus the two embryos are derived by different processes; the first is sexual and the other asexual (apomictic). The second embryo is, in reality, an internal bud that carries only the attributes of the plant that produced it. Both embryos may establish themselves as seedlings when the seed germinates. Many genera in this order produce flowers singly in the axil of a leaf (angle between stem and petiole). Others, as in the hollies, produce flower clusters (inflorescences), usually consisting of relatively few flowers. A model flower of this group possesses from four to six sepals, petals, and stamens (male) in each whorl. Sepals and petals may be partially united basally. The pistil (female) is composed of three to six carpels, differentiated into a basal, swollen ovary and a lobed, pollen-receptive stigma. Each chamber of the ovary, which is superior in position, produces two ovules. Following pollination and fertilization, the ovule becomes the seed and the ovary the fruit. In the hollies the fruit, though fleshy, is not a true berry; it is a drupe, or drupaceous berry. Among other families of the Celastrales, fruit types range from dry fruits that split in half to samaras (winged fruits). Several kinds of flowers may be produced in hollies and other members of the Celastrales. Male flowers, containing only functional stamens, and female flowers, in which only the pistil is fully developed, can occur on a plant that also produces perfect (bisexual) flowers. This diversity increases the chances of pollination. Seven families of this order develop a unique nectar-secreting disk placed below, between, or above the stamens. Disk position aids in distinguishing families from each other; hollies lack the disk. It is generally agreed that the four major families of this order form a coherent group. Many structural aspects of the minor families have not been studied in detail. Features unifying the families of the Celastrales include simple leaves, one or two ovules in each ovary chamber, and the presence of nectar disks near stamens. Families are separated on the basis of the following attributes: presence or absence of stipules; vine habit; type of inflorescence; distribution of staminate, pistillate, or perfect, flowers; structure of pistil; curvature of ovule; and the characteristics of the seed.