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This article is about oak trees and shrubs. OAK is also the three-letter IATA airport code for Oakland International Airport in Oakland, California USA.
Oaks
The term oak can be used as part of the common name of any of several hundred species of trees and shrubs in the genus
Quercus, and some related genera, notably Lithocarpus. The genus is native to the northern hemisphere, and includes deciduous and evergreen species extending from cold
latitudes to tropical Asia and America. The fruits of oaks are called acorns. The
"live oaks" - oaks with evergreen
leaves - are not a distinct group, instead with their members scattered among the sections below.
Classification
The genus is divided into two subgenera and a number of sections:
- Subgenus Quercus. Typical oaks. Widespread; acorns not tightly clustered, with scales on acorn cup
arranged in spirals.
- Section Quercus (synonym Lepidobalanus), the white oaks
of Europe, Asia and North America. Styles short; acorns mature in 6 months, sweet or slightly bitter, inside of acorn shell
hairless. Leaves mostly lack a bristle on lobe tips, which are usually rounded.
- Section Mesobalanus, the Hungarian oak and its relatives of Europe and Asia. Styles long; acorns mature in 6 months,
bitter, inside of acorn shell hairless (closely related to sect. Quercus and sometimes included in it).
- Section Cerris, the Turkey oak and its relatives of Europe and Asia. Styles long; acorns mature in 18 months, very
bitter, inside of acorn shell hairless. Leaves typically have sharp lobe tips, with bristles at the lobe tip.
- Section Protobalanus, the Canyon live oak and its relatives, in southwest USA & northwest Mexico. Styles short,
acorns mature in 18 months, very bitter, inside of acorn shell woolly. Leaves typically have sharp lobe tips, with bristles at
the lobe tip.
- Section Lobatae (synonym Erythrobalanus), the red oaks of
North, Central and northern South America. Styles long, acorns mature in 18 months, very bitter, inside of acorn shell woolly.
Leaves typically have sharp lobe tips, with bristles at the lobe tip.
- Subgenus Cyclobalanopsis. Cluster-acorn oaks. A large group of evergreen oaks in east Asia with
clustered acorns and the scales on the acorn cups in distinct concrescent rings (see photo, above right), often treated as a
separate genus Cyclobalanopsis.
List of Quercus
species
Uses
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timber of Quercus robur |
Oaks are hardwood trees, the wood
commonly used in furniture and flooring. The bark of Quercus suber, or
Cork oak, is used to produce wine stoppers (corks). This species grows in the Mediterranean Sea region, with Portugal, Spain, Algeria and Morocco producing most of the world's supply. Some European and American oak species are used to make barrels where wine and other spirits are aged; the barrels contribute to the taste. Of the
North American oaks, the most prized of the red oak group for lumber, all
of which is marketed as red oak regardless of the species of origin, is that of the Northern red oak, Quercus rubra (a.k.a. Q. borealis). The standard for the lumber of the
white oak group, all of which is marketed as white oak, is the White oak,
Quercus alba. White oak is often used for the construction of barrels for
aging wine. The wood of Quercus robur, the English oak and
Quercus petraea, the Sessile oak, is extensively used in
Europe. |
Cultivation
Oak acorns require stratification to stimulate sprouting. Most white oaks
need immediate stratification; indeed, species such as the Chestnut oak
(Quercus prinus) will sprout a root upon falling and must have a suitable substrate for immediate rooting. On the other
hand, many red oak acorns may be stratified for up to two years before
sprouting.
Diseases and pests
Sudden Oak Death (Phytophthora ramorum) is a water mould fungus that can kill oaks within just a few weeks.
Oak Wilt, caused by the fungus
Ceratocystis fagacearum (a fungus closely related to Dutch
Elm Disease), is also a lethal disease of some oaks, particularly the red oaks
(the white oaks can be infected but resist the disease better, and are not
usually killed). Other dangers include wood-boring beetles, as well as root rot in older trees which may not be apparent on the outside, often only being discovered when the
trees come down in a strong gale.
Historical note on Linnaean species
Linnaeus described only five species of oak from eastern North America, based on
general leaf form. These were White oak, Q. alba, Chestnut oak, Q. prinus, Red oak, Q. rubra, Willow
oak, Q. phellos, and Water oak, Q. nigra. Because he was dealing with confusing leaf forms, the Q.
prinus and Q. rubra specimens actually included mixed foliage of more than one species. For that reason, some
taxonomists in the past proposed different names for these two species (Q. montana and Q. borealis,
respectively) but the original Linnaean names have now been lectotypified with only the specimens in Linnaeus' herbarium that
refer to the species the names are applied to now.
See also
Trees of Britain, Trees of the world, Royal Oak
(tree)
External links
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