| Quercussubg. Quercus | |
|---|---|
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| Quercus robur (type species) growing in England | |
Scientific classification | |
| Kingdom: | Plantae |
| Clade: | Tracheophytes |
| Clade: | Angiosperms |
| Clade: | Eudicots |
| Clade: | Rosids |
| Order: | Fagales |
| Family: | Fagaceae |
| Genus: | Quercus |
| Subgenus: | Quercussubg. Quercus |
| Sections[2] | |
| |
Quercus subgenusQuercus is one of the twosubgenera into which the genusQuercus was divided in a 2017 classification (the other beingsubgenusCerris). It contains about 190 species divided among fivesections. It may be called the New World clade or the high-latitude clade; most species are native to the Americas, the others being found inEurasia and northernmostNorth Africa.
Members of subgenusQuercus are distinguished from members of subgenusCerris by few morphological features, their separation being largely determined bymolecular phylogenetic evidence. All are trees or shrubs bearingacorn-like fruit in which a cup covers at least the base of the nut. The outer structure of the maturepollen is one feature that distinguishes the two subgenera: in subgenusQuercus, the small folds or wrinkles (rugulae) are obscured bysporopollenin, whereas in subgenusCerris, the rugulae are visible or at most weakly obscured.[2]
The two subgenera are also distinguished to some extent by their different distributions. SubgenusQuercus occurs mainly in the Americas, with some species native toEurasia andNorth Africa, and may be called the New World clade or the high-latitude clade. SubgenusCerris is primarily Eurasian, with a few species in North Africa, and may be called the Old World clade or the mid-latitude clade.[2]
The followingcladogram summarizes the relationships that Denk et al. used to draw up their 2017 classification:[2]
| Quercus |
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Quercus sect.Lobatae was established byJohn Claudius Loudon in 1830.[3] The section, or part of it, has also been treated under names includingQuercus sect.RubraeLoudon andQuercus sect.ErythrobalanusSpach. It has also been treated as the subgenusErythrobalanus and as the full genusErythrobalanus(Spach) O.Schwarz. Its members may be called red oaks.[2]
Theperianth of thepistillate flowers has a characteristic flange-like shape. Thestaminate flowers have up to sixstamens. The stalk connecting the perianth to theovary is cone-shaped and often has rings. The acorns mature in two years, rarely in one year. The 'cup' (cupule) of the acorn is fused with its stalk (peduncule) forming a connective piece. Both the connective piece and the cup are covered with small triangular scales, mostly thin and membranous with broadly angled tips. The leaves typically have teeth with bristle-like extensions, or just bristles in leaves without teeth.[2]
The section contains about 125 species native toNorthern America (includingMexico),Central America, andColombia in South America.[2] The red oaks of Mexico are one of the groups of oaks that have most rapidly diversified into different species. Molecular evidence suggests that there are significant numbers of undescribedQuercus species in Mexico, so the number of known species in the section is likely to be an underestimate of the total diversity.[4]
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Quercus sect.Protobalanus was first established as a subgenus byWilliam Trelease in 1922 and then later treated as a section byOtto Karl Anton Schwarz in 1936 andAimée Antoinette Camus in 1938.[2][note 1]
Thestaminate flowers have eight to tenstamens. Thepollen ornamentation has only small wrinkles or folds (verrucae). The acorns mature after two years. The cup (cupule) at the base of the acorn has triangular scales that are fused at the base and have sharp angled tips. The scales are thick and compressed into rings, often forming small bumps, that may be obscured by glandular hairs. The leaf teeth end in spines.[2]
The section contains only five species, native to southwestern North America and northwestern Mexico.[2]
Quercus sect.Ponticae was first established byBoris Stefanoff in 1930. It has also been treated as a subsection and a series, including under the nameQ. ser.SadlerianaeTrelease.[2]
Species are shrubs or small trees, withrhizomes. Thestaminatecatkins are up to 10 cm long. The cup (cupule) at the base of the acorn has scales with sharp angled ends. The leaves are either evergreen or deciduous, with simple or compound teeth. The leaf buds are large, enclosed in loosely attached scales.[2]
There are only two species,Quercus pontica andQuercus sadleriana.[5] They have disjoint distributions.Quercus pontica is native to mountainous areas of north-easternTurkey and westernGeorgia.Quercus sadleriana is native to northern-mostCalifornia and southern-mostOregon in the United States.[2]
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Quercus sect.Virentes was first established byJohn Claudius Loudon in 1838. It has also been treated as a series.[2] Members of the section may be called live oaks.[6]
Species are trees orrhizomatous shrubs. They areevergreen orbrevideciduous. The acorns mature in a year. The cup at the base of the acorn has narrowly triangular scales, with thin keels, at most small bumps (tubercules), and sharp angled ends. The leaves are evergreen or almost so. A distinctive feature of the section is that the germinating seed has fused seed leaves (cotyledons) and an elongated stem above the cotyledons (theepicotyl) that forms a tube, while the stem below the cotyledons (thehypocotyl) istuberous.[2]
The section contains seven species, native to south-eastern Northern America, Mexico, the West Indies (Cuba), and Central America.[2]
Quercus sect.Quercus has been known, either in whole or part, by a variety of names in the past, includingQuercus sect. Albae,Quercus sect. Macrocarpae andQuercus sect. Mesobalanus. Members of the section may be called white oaks. The section includes all white oaks from North America (treated by Trelease as subgenusLeucobalanus).[2]
Thestaminate flowers have seven or morestamens. Theacorns mature in one year. The seed leaves (cotyledons) are either free or fused together. The cup at the base of the acorn has thickened triangular scales that are either free or fused at the base and have sharp angled tips. The scales have keels and are often covered with small bumps (tuberculate). The leaf teeth typically do not have either bristle-like or spiny tips.[2]
There are about 150 species, native to Northern America, Mexico, Central America, westernEurasia, East Asia, and North Africa.[2]
_on_a_White_Oak_within_a_wooded_area_in_the_Franklin_Farm_section_of_Oak_Hill%2c_Fairfax_County%2c_Virginia.jpg)
