Quercus subgenus Cerris is one of the two subgenera into which the genus Quercus was divided in a 2017 classification (the other being subgenus Quercus). It contains about 140 species divided among three sections. It may be called the Old World clade or the mid-latitude clade; all species are native to Eurasia and North Africa. Description 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 featurs, 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 western Eurasia), 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. Phylogeny The following cladogram summarizes the relationships that Denk et al. used to draw up their 2017 classification: Section Cyclobalanopsis Quercus sect. Cyclobalanopsis was first established, as the genus Cyclobalanopsis, by Anders Sandøe Ørsted in 1867. 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, or ring-cup oaks. Like all species of Quercus, those of section Cyclobalanopsis are trees or shrubs with acorn-like fruit. The staminate flowers are arranged in groups of usually one to three, but sometimes up to seven, along the axis of the inflorescence. The ornamentation of the mature pollen is a distinguishing feature of the section: