Cyclobalanopsis

''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 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.

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: pollen grains have vertical folds (rugulae). The stalk that joins the perianth to the ovary (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.

The section contains about 90 species native to tropical and subtropical Asia including the southern Himalayas.

File:黃背櫟 Quercus championii -香港西貢獅子會自然教育中心 Saikung, Hong Kong- (9219901913).jpg, Catkins of '' Quercus championii'' in Hong Kong
File:Quercus lamellosa.jpg, Illustration of '' Quercus lamellosa'' with acorns
File:Quercus miyagii.JPG, '' Quercus miyagii'' in habitat
File:Chêne au bois de Vaires.jpg, '' Quercus sessilifolia'' in cultivation in France
File:Arisan Oak 2016.png, Leaves and acorns of '' Quercus stenophylloides''

Section ''Ilex''

''Quercus'' sect. ''Ilex'' was first established by John Claudius Loudon in 1838. It has also been treated as a subgenus, under the name ''Quercus'' subg. ''Heterobalanus'' Oerst., and as subsection. Members may be called ilex oaks.

Like all species of ''Quercus'', those of section ''Ilex'' are trees or shrubs with acorn-like fruit. The staminate flowers have four to six stamens. The ornamentation of the mature pollen 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.

The section contains about 40 species native to Eurasia and North Africa.

File:Golden oak.JPG, '' Quercus alnifolia''
File:Quercus coccifera.jpg, Acorns of ''Quercus coccifera''
File:Quercus floribunda.jpg, '' Quercus floribunda''
File:Quercus ilex0.jpg, Leaves and catkins of ''Quercus ilex''
File:Quercus ilex rotundifolia.jpg, '' Quercus rotundifolia''

Section ''Cerris''

''Quercus'' section ''Cerris'' was first established by Barthélemy Charles Joseph Dumortier in 1829. It has been treated as a section under other names, including ''Quercus'' sect. ''Erythrobalanopsis'' Oerst., ''Quercus'' sect. ''Castaneifolia'' O.Schwarz, ''Quercus'' sect. ''Vallonea'' O.Schwarz, ''Quercus'' sect. ''Aegilops'' (Reichenb.) O.Schwarz and the illegitimate name ''Quercus'' sect. ''Eucerris'' Oerst. Members may be called cerris oaks.

Like all species of ''Quercus'', those of section ''Cerris'' are trees or shrubs with acorn-like fruit. The staminate flowers have four to six stamens. The ornamentation of the mature pollen 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.

There are about 13 species in Eurasia and North Africa, including the cork oak, ''Quercus suber'', an important source of cork for wine stoppers, among other uses. It is the only oak section with a centre of diversity in the Western Palearctic.

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

{{taxonbar, from1=Q116884314, from2=Q6123078, from3=Q116858648, from4=Q116884274

subg. Cerris
Plant subgenera