Quercus Sect. Quercus

''Quercus'' subgenus ''Quercus'' is one of the two subgenera into which the genus ''Quercus'' was divided in a 2017 classification (the other being subgenus ''Cerris''). It contains about 190 species divided among five sections. It may be called the New World clade or the high-latitude clade; most species are native to the Americas, the others being found in Eurasia and northernmost North Africa.

Description

Members of subgenus ''Quercus'' are distinguished from members of subgenus ''Cerris'' by few morphological features, their separation being largely determined by molecular phylogenetic evidence. All are trees or shrubs bearing acorn-like fruit in which a cup covers at least the base of the nut. The outer structure of the mature pollen is one feature that distinguishes the two subgenera: in subgenus ''Quercus'', the small folds or wrinkles (rugulae) are obscured by sporopollenin, whereas in subgenus ''Cerris'', the rugulae are visible or at most weakly obscured.

The two subgenera are also distinguished to some extent by their different distributions. Subgenus ''Quercus'' occurs mainly in the Americas, with some species native to Eurasia and North Africa, and may be called the New World clade or the high-latitude clade. 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.

Taxonomy

Phylogeny

The following cladogram summarizes the relationships that Denk et al. used to draw up their 2017 classification:

Section ''Lobatae''

''Quercus'' sect. ''Lobatae'' was established by John Claudius Loudon in 1830. The section, or part of it, has also been treated under names including ''Quercus'' sect. ''Rubrae'' Loudon and ''Quercus'' sect. ''Erythrobalanus'' Spach. It has also been treated as the subgenus ''Erythrobalanus'' and as the full genus ''Erythrobalanus'' (Spach) O.Schwarz. Its members may be called red oaks.

The perianth of the pistillate flowers has a characteristic flange-like shape. The staminate flowers have up to six stamens. The stalk connecting the perianth to the ovary 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.

The section contains about 125 species native to Northern America (including Mexico), Central America, and Colombia in South America. 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 undescribed ''Quercus'' species in Mexico, so the number of known species in the section is likely to be an underestimate of the total diversity.

File:028 quercus castanea.jpg, ''Quercus castanea''
File:Northern Pin Oak.jpg, Leaves of ''Quercus ellipsoidalis''
File:Quercus myrtifolia mosbo6.jpg, ''Quercus myrtifolia'' growing as a shrub
File:Red Oak, Prokocim, Krakow, Poland.jpg, ''Quercus rubra'' in autumn (in cultivation)

Section ''Protobalanus''

''Quercus'' sect. ''Protobalanus'' was first established as a subgenus by William Trelease in 1922 and then later treated as a section by Otto Karl Anton Schwarz in 1936 and Aimée Antoinette Camus in 1938.

The staminate flowers have eight to ten stamens. The pollen 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.

The section contains only five species, native to southwestern North America and northwestern Mexico.

File:Quercus cedrosensis 53513896.jpg, ''Quercus cedrosensis'' in habitat in Mexico
File:Quercus chrysolepis 08638.JPG, ''Quercus chrysolepis'' leaves showing spines
File:Quercus chrysolepis acorns.jpg, ''Quercus chrysolepis'' acorns
File:Island Oak in Santa Rosa Island.jpg, ''Quercus tomentella'' in habitat on Santa Rosa Island, California
File:Quercus tomentella acorn.JPG, ''Quercus tomentella'' acorn

Section ''Ponticae''

''Quercus'' sect. ''Ponticae'' was first established by Boris Stefanoff in 1930. It has also been treated as a subsection and a series, including under the name ''Q.'' ser. ''Sadlerianae'' Trelease.

Species are shrubs or small trees, with rhizomes. The staminate catkins 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.

There are only two species, ''Quercus pontica'' and ''Quercus sadleriana''. They have disjoint distributions. ''Quercus pontica'' is native to mountainous areas of north-eastern Turkey and western Georgia. ''Quercus sadleriana'' is native to northern-most California and southern-most Oregon in the United States.

File:Quercus pontica-5.jpg, ''Quercus pontica'' in habitat
File:Flickr - brewbooks - Quercus sadleriana (Deer Oak).jpg, ''Quercus sadleriana'' in cultivation

Section ''Virentes''

''Quercus'' sect. ''Virentes'' was first established by John Claudius Loudon in 1838. It has also been treated as a series. Members of the section may be called live oaks.

Species are trees or rhizomatous shrubs. They are evergreen or brevideciduous. 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 (the epicotyl) that forms a tube, while the stem below the cotyledons (the hypocotyl) is tuberous.

The section contains seven species, native to south-eastern Northern America, Mexico, the West Indies (Cuba), and Central America.

Section ''Quercus''

''Quercus'' sect. ''Quercus'' has been known, either in whole or part, by a variety of names in the past, including ''Quercus'' sect. ''Albae'', ''Quercus'' sect. ''Macrocarpae'' and ''Quercus'' sect. ''Mesobalanus''. Members of the section may be called white oaks. The section includes all white oaks from North America (treated by Trelease as subgenus ''Leucobalanus'').

The staminate flowers have up to seven stamens. The acorns 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.

There are about 150 species, native to Northern America, Mexico, Central America, western Eurasia, East Asia, and North Africa.

File:Keeler Oak Tree - distance photo, May 2013.jpg, Large ''Quercus alba'' growing in New Jersey
File:2021-04-22 18 54 32 Male flowers (catkins) on a White Oak within a wooded area in the Franklin Farm section of Oak Hill, Fairfax County, Virginia.jpg, ''Quercus alba'' catkins (staminate or 'male' flowers)
File:Leaves of California Scrub Oak.JPG, ''Quercus berberidifolia'' in habitat in California
File:Quercus lusitanica - Köhler–s Medizinal-Pflanzen-253.jpg, Illustration of ''Quercus lusitanica'' showing staminate (left) and pistillate flowers (top right)
File:Chestnut Oak in Weiser State Forest.JPG, ''Quercus montana'' in Pennsylvania
File:Wintereik Engeland.jpg, ''Quercus petraea'' in England, about 300 years old
File:Летен дъб - цъфтеж, нови листа.JPG, New leaves and pistillate ('female') flowers of ''Quercus robur''
File:Chêne glands.jpg, ''Quercus robur'' leaves and acorns

Notes

References

{{Taxonbar, from=Q4163388

Plant subgenera
subg. Quercus