Quercus subg. Cerris

Like all species of Quercus, those of subgenus Cerris are trees or shrubs with acorn-like fruit in which a cup covers at least the base of the nut. Members of subgenus Cerris are distinguished from members of subgenus Quercus by few morphological features, their separation being largely determined by molecular phylogenetic evidence. The structure of the mature pollen is one feature that distinguishes the two subgenera: in subgenus Cerris, the small folds or wrinkles (rugulae) are visible or at most weakly obscured, whereas in subgenus Quercus, the rugulae are obscured by sporopollenin. The two subgenera are also distinguished to some extent by their different distributions. Subgenus Cerris is primarily Eurasian, with a few species in North Africa, and may be called the Old World clade or the mid-latitude clade. Subgenus Quercus occurs mainly in the Americas (although some species are also found in Eurasia and North Africa), and may be called the New World clade or the high-latitude clade. ==Taxonomy==

Quercus subgenus Cerris was first established by Anders Sandøe Ørsted in 1867. However, his conception and that of later workers, who often reduced it to a section, was closer to the modern section Cerris than the wider circumscription that has resulted from molecular phylogenetic studies, in which the subgenus is one of two divisions of the genus Quercus, and includes three sections. It was first reduced from a genus to a section by George Bentham and William Jackson Hooker in 1880. It has also been treated as a subgenus. Members may be called cycle-cup oaks, File:Цер 13.jpg|Quercus cerris in autumn File:Quercus cerris 5.jpg|Acorns of Quercus cerris File:Gland and cupule of Valonia oak - panoramio.jpg|Acorn of Quercus ithaburensis subsp. macrolepis, the valonia oak File:Quercus libani port.jpg|Quercus libani File:Denuded cork oak (2874384025).jpg|Trunk of Quercus suber, the cork oak, after harvesting ==Conservation==

The 2020 Red List of Oaks shows that within the species assessed across all eight sections of the genus Quercus, the sections Cyclobalanopsis and Ilex have the largest proportions of species put into the "critically endangered" category, representing the highest level of threat. A large number of section Cyclobalanopsis species occur in China: the Flora of China states that 69 are native to China of which 43 are endemic. China has the largest number of threatened oak species. ==References==