Oak

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This article is about oaks (Quercus). For other uses of "Oak" or "Oak tree", see Oak (disambiguation)

{{Taxobox | color = lightgreen | name = Oaks | image = Quercus robur.jpg | image_width = 240px | image_caption = Foliage and acorns of Quercus robur | regnum = Plantae | divisio = Magnoliophyta | classis = Magnoliopsida | ordo = Fagales | familia = Fagaceae | genus = Quercus | genus_authority = L. | subdivision_ranks = Species | subdivision = See List of Quercus species }}

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 Cyclobalanopsis and 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.

1 Classification
2 Uses
3 Cultivation
4 Diseases and pests
5 Cultural significance
6 Historical note on Linnaean species
7 Gallery
8 External links

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Classification

The genus is divided into a number of sections:

Section Quercus (synonyms Lepidobalanus and Leucobalanus), 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.

Full list of Quercus species

Image:Quercus stellata.jpg Hybrids are common in oaks, but only between species within the same section; no verified inter-section hybrids are known.

The genus Cyclobalanopsis, here treated as a distinct genus following the Flora of China, is often included within Quercus as a distinct subgenus.

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Uses

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, which are in some cases charred before use, 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.

The bark of the White Oak is dried and used in medical preparations. Oak bark is also rich in tannin, and is used by tanners for tanning leather. Acorns are used for making flour or roasted for acorn coffee.

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Cultivation

Oak catkins are made up of small, yellowish-green flowers. Acorns appear after the female flowers are fertilized in spring. They are typical brown, tan, yellow, light green, deep green or grayish green. Oaks grow slowly and usually don’t bear acorns until they are about 20 years old. 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. The lifespan of an oak typically ranges from 200 to 600 years.

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Diseases and pests

Sudden Oak Death (Phytophthora ramorum) is a water mould 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 generally live longer). 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. Oaks are used as food plants by the larvae of a large number of Lepidoptera species - see list of Lepidoptera which feed on Oaks.

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Cultural significance

Image:5ec ger.png The oak is a common symbol of strength and endurance, and is the national tree of the United Kingdom, Germany and the United States.

A number of individual oak trees, such as the Royal Oak in Britain and the Charter Oak in the United States, are of great historical or cultural importance; for a list of important oaks, see Individual oak trees.

There is also a proverb, 'Mighty oaks from tiny acorns grow'.

Iowa designated the oak as the official state tree in 1961.

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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.

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