Fagaceae

The family Fagaceae, or beech family, comprises about 900 species of both evergreen and deciduous trees and shrubs, which are characterized by alternate simple leaves with pinnate venation, unisexual flowers in the form of catkins, and fruit in the form of cup-like (cupule) nuts. Fagaceous leaves are often lobed and both petioles and stipules are generally present. Fruits lack endosperm and lie in a scaly or spiny husk that may or may not enclose the entire nut, which may consist of one to seven seeds. The best-known group of this family is the oaks, genus Quercus, the fruit of which is a non-valved nut (usually containing one seed) called an acorn. The husk of the acorn in most oaks only forms a cup in which the nut sits.

Several members of the Fagaceae have important economic uses. Many species of oak, chestnut, and beech (genera Quercus, Castanea, and Fagus respectively) are commonly used as timber for floors, furniture, cabinets, and wine barrels. Cork for stopping wine bottles and a myriad of other uses is made from the bark of cork oak, Quercus suber. Chestnuts, a tasty treat enjoyed by many in the winter, are the fruits from species of the genus Castanea. Numerous species from several genera are prominent ornamentals, and wood chips from the genus Fagus are often used in flavoring beers.

Classification

The Fagaceae are often divided into three or four subfamilies and are generally accepted to include nine or ten genera (listed below). Monophyly of the Fagaceae is strongly supported by both morphological (especially fruit morphology) and molecular data.

The Southern Hemisphere genus Nothofagus, commonly the southern beeches, was historically placed in the Fagaceae sister to the genus Fagus, but recent molecular evidence suggests otherwise. While Nothofagus shares a number of common characteristics with the Fagaceae, such as cupule fruit structure, it differs significantly in a number of ways including distinct stipule and pollen morphology as well as having a different number of chromosomes. The currently accepted view by systematic botanists is to place Nothofagus in its own family, Nothofagaceae.

Genera

Castanea - Chestnuts; eight species, north temperate east Asia, southwest Asia, southeast Europe, eastern North America
Castanopsis - chinquapins or chinkapins about 125-130 species, southeast Asia
Chrysolepis - Golden chinkapins; two species, western USA
Colombobalanus - one species C. excelsa, northern South America, often included in Trigonobalanus
Fagus - Beeches; 10 species, north temperate east Asia, southwest Asia, Europe, eastern North America
Formanodendron - one species F. doichangensis, southeast Asia, often included in Trigonobalanus
Lithocarpus - Tanoaks or Stone oaks; about 330-340 species, all but one in warm temperate to tropical Asia, the one (L. densiflorus) in California and southwest Oregon
Quercus - Oaks; about 500 species, widespread Northern Hemisphere, crossing the equator in Indonesia
Trigonobalanus - one species T. verticillata, tropical southeast Asia (three species if Colombobalanus and Formanodendron included)

The Quercus subgenus Cyclobalanopsis is treated as a distinct genus by the Flora of China, but as a subgenus by most taxonomists.

The genus Nothofagus (Southern beeches; about 35 species from the Southern Hemisphere), formerly included in the Fagaceae, is now treated in the separate family Nothofagaceae.

Distribution

The Fagaceae are widely distributed across the Northern Hemisphere. Genus-level diversity is concentrated in Southeast Asia, where most of the extant genera are thought to have evolved before migrating to Europe and North America (via the Bering Land Bridge). Members of the Fagaceae (such as Fagus grandifolia, Castanea dentata and Quercus alba in the Northeastern United States, or Fagus sylvatica, Quercus robur and Q. petraea in Europe) are often ecologically dominant in Northern temperate forests.