| Quercussubg. Cerris | |
|---|---|
 | |
| Quercus cerris (type species) | |
Scientific classification | |
| Kingdom: | Plantae |
| Clade: | Tracheophytes |
| Clade: | Angiosperms |
| Clade: | Eudicots |
| Clade: | Rosids |
| Order: | Fagales |
| Family: | Fagaceae |
| Genus: | Quercus |
| Subgenus: | Quercussubg. Cerris Oerst.[1] |
| Sections[1] | |
| |
Quercus subgenusCerris is one of the twosubgenera into which the genusQuercus was divided in a 2017 classification (the other beingsubgenusQuercus). It contains about 140 species divided among threesections. It may be called the Old World clade or the mid-latitude clade; all species arenative toEurasia andNorth Africa.
Like all species ofQuercus, those of subgenusCerris are trees or shrubs withacorn-like fruit in which a cup covers at least the base of the nut. Members of subgenusCerris are distinguished from members of subgenusQuercus by few morphological features, their separation being largely determined bymolecular phylogenetic evidence. The structure of the mature pollen is one feature that distinguishes the two subgenera: in subgenusCerris, the small folds or wrinkles (rugulae) are visible or at most weakly obscured, whereas in subgenusQuercus, the rugulae are obscured bysporopollenin.[1]
The two subgenera are also distinguished to some extent by their different distributions. SubgenusCerris is primarilyEurasian, with a few species inNorth Africa, and may be called the Old World clade or the mid-latitude clade. SubgenusQuercus 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.[1]
Quercus subgenusCerris was first established byAnders Sandøe Ørsted in 1867. However, his conception and that of later workers, who often reduced it to a section, was closer to the modern sectionCerris than the widercircumscription that has resulted from molecular phylogenetic studies, in which the subgenus is one of two divisions of the genusQuercus, and includes three sections.[1]
The followingcladogram summarizes the relationships that Denk et al. used to draw up their 2017 classification:[1]
| Quercus |
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Quercus sect.Cyclobalanopsis was first established, as the genusCyclobalanopsis, byAnders Sandøe Ørsted in 1867.[2] It was first reduced from a genus to a section byGeorge Bentham andWilliam Jackson Hooker in 1880. It has also been treated as a subgenus. Members may be called cycle-cup oaks,[1] or ring-cup oaks.
Like all species ofQuercus, those of sectionCyclobalanopsis are trees or shrubs with acorn-like fruit. Thestaminate flowers are arranged in groups of usually one to three, but sometimes up to seven, along the axis of theinflorescence. The ornamentation of the maturepollen is a distinguishing feature of the section: pollen grains have vertical folds (rugulae). The stalk that joins theperianth to theovary (the perianthopodium) has three to five distinct rings. The 'cup' (cupule) around the base of acorn also has distinct rings formed from thin membranes (lamellae), which also distinguishes the section from other oaks. The leaves are evergreen.[1]
The section contains about 90 species native to tropical and subtropical Asia including the southern Himalayas.[1]
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Quercus sect.Ilex was first established byJohn Claudius Loudon in 1838. It has also been treated as a subgenus, under the nameQuercus subg.HeterobalanusOerst., and as subsection. Members may be called ilex oaks.[1]
Like all species ofQuercus, those of sectionIlex are trees or shrubs with acorn-like fruit. Thestaminate flowers have four to six stamens. The ornamentation of the maturepollen is distinctive, consisting of wrinkles or folds (rugulae). The acorns mature either annually or after two years. The cup of the acorn has triangular scales, usually thin and membranous. The toothed leaves are evergreen with spines or bristles at the ends of the teeth.[1]
The section contains about 40 species native to Eurasia and North Africa.[1]
Quercus sectionCerris was first established byBarthélemy Charles Joseph Dumortier in 1829. It has been treated as a section under other names, includingQuercus sect.ErythrobalanopsisOerst.,Quercus sect.CastaneifoliaO.Schwarz,Quercus sect.ValloneaO.Schwarz,Quercus sect.Aegilops(Reichenb.) O.Schwarz and theillegitimate nameQuercus sect.EucerrisOerst. Members may be called cerris oaks.[1]
Like all species ofQuercus, those of sectionCerris are trees or shrubs with acorn-like fruit. Thestaminate flowers have four to six stamens. The ornamentation of the maturepollen is distinctive, consisting of scattered small bumps (verrucate). The cup of the acorn has narrowly triangular scales, thickened and with a keel and elongated recurved tips. The leaf is toothed, typically with bristle-like extensions to the teeth.[1]
There are about 13 species in Eurasia and North Africa,[1] including the cork oak,Quercus suber,[3] an important source ofcork for wine stoppers,[4] among other uses. It is the only oak section with a centre of diversity in theWestern Palearctic.[5]
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The 2020Red List of Oaks shows that within the species assessed across all eight sections of the genusQuercus, the sectionsCyclobalanopsis andIlex have the largest proportions of species put into the "critically endangered" category, representing the highest level of threat.[6] A large number of sectionCyclobalanopsis species occur in China: theFlora of China states that 69 are native to China of which 43 are endemic.[7] China has the largest number of threatened oak species.[6]