SAPINDALES

order of flowering plants that includes the citrus and other species important for their fruits. Most of its members are trees (some of which are prized as sources of timber), shrubs, and woody vines. The Sapindales order consists of 15 families, about 500 genera, and some 6,200 species. More than half of the species belong to just two families, the Sapindaceae and the Rutaceae. Six other families account for most of the remaining species in the order. The Sapindales order is mostly tropical and subtropical, with many species occurring in rain forests below elevations of 2,000 m (6,600 feet). Soapberry (Sapindus saponaria). The soapberry family (Sapindaceae) has about 2,000 species found throughout the wet tropics of the world; the family is especially abundant in the American tropics. (See photograph.) Among the family's edible tropical fruits are the litchi (Litchi chinensis), rambutan (Nephelium lappaceum), longan (Euphoria longana), akee (Blighia sapida), Spanish lime (Melicoccus bijugus), and Senegal cherry (Aphania senegalensis). The soapberries (genus Sapindus) are important as soap substitutes because of the presence of saponins (chemical substances that produce soapy lathers). The citrus, or rue, family (Rutaceae) has about 1,700 species of trees and shrubs. They are widespread in distribution but occur primarily in tropical and warm-temperate areas. Its best-known members are in the genus Citrus and have spread worldwide. The small trees in this genus include the lime (C. aurantifolia), lemon (C. limon), several types of orange, and the grapefruit (C. paradisi). Poison oak (Toxicodendron diversiloba). The sumac family (Anacardiaceae) has about 650 species, among them various sumac (Rhus) shrubs valued as ornamentals. Other members of the family produce the mango (Mangifera indica), cashew (Anacardium occidentale), and pistachio nut (Pistacia vera). Members of the genus Toxicodendron produce resins that cause contact dermatitis in humans, the most notorious being poison oak (T. diversiloba; see photograph), poison sumac (T. vernix), and poison ivy (T. radicans). The frankincense family (Burseraceae) has about 600 species, many of them dominant plants in tropical forests. They are also known for their aromatic gums or resins, such as frankincense and myrrh. The mahogany family (Meliaceae), with about 575 species, is best known for its timber trees, including many mahogany species belonging to various genera. The maple family (Aceraceae), with about 200 species, is not a large family, but its trees dominate areas of forest throughout the North Temperate Zone, from North America through Europe to China and Japan. The best-known tree of the family is the sugar maple (Acer saccharum) of North America. The horse chestnut family (Hippocastanaceae) contains the buckeyes (Aesculus) and the horse chestnut (A. hippocastanum), used for paper pulp and as ornamental and shade trees. Most species of Sapindales have pinnately compound leaves that are arranged alternately along the stem. Pollination for most of the Sapindales appears to be accomplished by insects. Many species are unisexual (i.e., male and female flowers are borne on separate plants), while many others bear both bisexual and male or female flowers on the same plant. The fruit in Sapindales is usually a capsule that splits open between internal partitions. order of dicotyledonous flowering plants, a division of the subclass Rosidae. It includes the citrus and other species important for their fruits. Most of its members are trees (some of which are prized as sources of timber), shrubs, and woody vines. The order Sapindales consists of 15 families, approximately 500 genera, and some 6,200 species. More than half of the species belong to 2 families, the Sapindaceae (with 2,000 species) and the Rutaceae (with 1,700 species). Most of the remaining species belong to 6 other well-known families, the Anacardiaceae (with 650 species), Burseraceae (with 600 species), Meliaceae (with 575 species), Zygophyllaceae (with 270 species), Aceraceae (with 200 species), and Simaroubaceae (with 150 species). The remaining 7 families together total fewer than 100 species. Additional reading Terence D. Pennington, Meliaceae (1981), a monographic treatment of the New World members of the ecologically and economically important mahogany family; Peter G. Waterman and Michael F. Grundon (eds.), Chemistry and Chemical Taxonomy of the Rutales (1983), an excellent example of how chemistry can be used to aid in classification; D.M. Porter, Disjunct Distributions in the New-World Zygophyllaceae, Taxon, 23(2/3):339346 (1974); M.F. Das Gracas Fernandes da Silva, O.R. Gottlieb, and F. Ehrendorfer, Chemosystematics of the Rutaceae: Suggestions for a More Natural Taxonomy and Evolutionary Interpretation of the Family, Plant Systematics and Evolution, 161(34):97134 (1988); Steven Nagy, Philip E. Shaw, and Matthew K. Veldhuis (eds.), Citrus Science and Technology, 2 vol. (1977); papers in the Journal of the Arnold Arboretum on sapindalian genera: G.K. Brizicky, The Genera of Sapindales in the Southeastern United States, 44:462501 (1963), a thorough discussion of the Aceraceae, Hippocastanaceae, and Sapindaceae of the area, The Genera of Rutaceae in the Southeastern United States, 43:122 (1962), The Genera of Simaroubaceae and Burseraceae in the Southeastern United States, 43:173186 (1962), and The Genera of Anacardiaceae in the Southeastern United States, 43:359375 (1962); S. Spongberg, The Staphyleaceae in the Southeastern United States, 52:196203 (1971); D.M. Porter, The Genera of Zygophyllaceae in the Southeastern United States, 53:531552 (1972).