Infrageneric classification of Quercus (Fagaceae) and typification of sectional names

Abstract

The genus Quercus L (the true oaks) is widespread in the Northern hemisphere, in habitats ranging from temperate and tropical forests to dry thorn scrub and semi-desert. As far as is known, all species are anemophilous. The genus is most closely related to Trigonobalanus Forman, Colombobalanus Nixon and Crepet, and Formanodendron Nixon and Crepet, 3 extant tropical monotypic genera. The oldest unequivocal oak fossils are Oligocene in age, although fossilized catkins and stellate trichomes that may represent earlier Quercus are preserved in Baltic amber, of uncertain Early Tertiary age. Trigonobalanoid fossils are known from the Oligocene and Paleocene of North America, and later deposits in Europe. A subgeneric and sectional classification of Quercus that is slightly modified from that proposed by Camus is most consistent with recent phylogenetic analyses within Quercus. Such a classification recognizes 2 subgenera, Quercus and Cyclobalanopsis (Oersted) Schneider. The latter is restricted to eastern Asia and Malesia. Subgenus Quercus is divided into sections Lobatae Loudon (red oaks: North and South America), Protobalanus (Trelease) Schwarz (intermediate oaks: western North America), and Quercus (white oaks: E and W hemispheres). Two groups of white oaks that are sometimes recognized as sections, Ilex (Eurasia), and Cerris (Eurasia) are considered part of section Quercus, but merit subsectional or higher rank following more complete analyses.