Introduction to Oak
Oak, a genus of trees and shrubs. There are about 900 species of oaks, 75 of which are found in North America.
Oaks are deciduous or evergreen, depending on the species They have lustrous green leaves with lobed or toothed edges. Most species of oak grow in well-drained soil. The bark of most oaks is either light gray and scaly or blackish-brown and furrowed. Oaks are planted as shade trees, for their foliage and symmetrical crown.
The live oak lives about 300 years and grows up to 50 feet tall.Oaks produce small, greenish flowers in the spring. Male and female flowers are borne on the same branch. The male flowers grow in catkinsdrooping clusters that hang down from the branch. The female flowers grow in spikes. The flowers are pollinated by the wind.
All oaks bear fruit called acorns. The acorn is a nut, a dry fruit that contains a single seed covered with a hard outer coat. A portion of the outer coat is contained in a cup, or cupule. The cup is composed of tiny scales called bracts.
Oaks are susceptible to a number of diseases. Oak wilt, a fungal disease, causes the leaves to die and drop off, and the tree eventually dies. Oaks are attacked by moths and gall-forming insects.
Oaks are prized for their tough, durable wood. It is used for such things as flooring, paneling, furniture, railroad ties, barrels, and tool handles, and in shipbuilding. Cork is made from the outer bark of the cork oak of southern Europe and North Africa.
Acorns provide food for small mammals and birds. They were formerly a staple of North American Indians. Acorns are often mixed with other nuts to form mast, a food for hogs and other livestock.
The oak is the state tree of Iowa; the white oak, of Connecticut, Illinois, and Maryland the live oak, of Georgia; and the red oak, of New Jersey.
Types of Oaks
Oaks form the genus Quercus of the beech family, Fagaceae. There are three main divisions in the genus: the Asiatic evergreen subgenus, the white oak subgenus, and the black oak subgenus. The Asiatic subgenus includes the greatest number of oak species and is distinct because the bracts of the acorn cups of these oaks are arranged in concentric rings. A few Asiatic species are grown in the United States as ornamental trees.
The North American oaks are members of the two remaining subgenera, the white oak and black oak groups. The bracts of the acorn cups of these subgenera overlap in a shinglelike pattern. Species of the white oak group produce acorns every year, while species of the black oak group produce acorns every other year. Many of the common names of oaks are used for more than one species.
The White Oak Group
The White Oak group includes two-thirds of the oak species native to the United States, a few of which are evergreen. Most of the deciduous species are found in the eastern two-thirds of the country. The evergreen species grow in southern and far western areas where there is moderate winter weather and an adequate supply of water. The tips of the lobes of the leaves of most white oak species are smooth and rounded. Among the common species of the white oak group are:
White Oak,an 80- to 100-foot (24- to 30-m) tree with deeply lobed leaves and oval acorns about one inch (2.5 cm) long. Its acorns are edible. The white oaks are found from Maine to Florida and west to Minnesota and Texas. They live an extremely long time, some for up to 800 years. These oaks have the hardest, most durable wood of all oaks and are the most important lumber species.
The white oak is Quercus alba.
Bur Oak,the oak having the largest acorns. The bur oak grows in southern Canada and the northeastern United States west to Montana and south to Texas. This 50- to 80-foot (15- to 24-m) tree has almost spherical acorns that are up to 2 inches (5 cm) long and are almost completely covered by the fringed cup. The wedge-shaped leaves are deeply lobed at the narrow stem end and shallowly lobed in the wide portion. They are 4 to 10 inches (10 to 25 cm) long.
The bur oak is Q. macrocarpa.
Chinkapin Oak,a tree that grows up to 80 feet (24 m) tail and is found in the eastern two-thirds of the United States. Its acorns are oval and up to 1 inch (2.5 cm) long. The toothed leaves, 4 to 6 inches (10 to 15 cm) long, are yellowish-green on the upper side and silvery-white beneath.
The chinkapin oak is Q. muehlenbergii.
Chestnut Oak,an oak with toothed leaves, 4 to 8 inches (10 to 20 cm) long, that resemble those of the chestnut tree. The chestnut oak grows up to 80 feet (24 m) tall and is found east of the Mississippi River * am Maine to Alabama and north to Michigan. Its acorns are oval and about one inch (2.5 cm) long.
The chestnut oak is Q. prinus.
Live Oak,an evergreen oak. The common live oak lives about 300 years, grows up to 50 feet (IS m) tall, and is found from Virginia south to Florida and west along the coast to Mexico. It has smooth-edged, oblong leaves 1 1/2 to 4 inches (3.8 to 10 cm) long. Other live oaks are the California live oak and the canyon live oak, both native to California.
The live oak is Q. virginiana; the California live oak, Q. agrifolia; and the canyon live oak, Q. chrysolepis.
Post Oak,a hardy oak that grows up to 70 feet (21 m) tall in the center of its range, but is a shrub in its northern reaches. The post oak is found from Massachusetts to Florida and west to Texas. Its lobed leaves are 4 to 6 inches (10 to 15 cm) long and are darker on the upper surface than beneath. The acorns are oval and about 3/4 inch (2 cm) long. The post oak grows in relatively dry soil that may be rocky or sandy.
The post oak is Q. stellata.
Scrub Oak,any of several shrubby oaks that grow up to 20 feet (6 m) tall. There are scrub oaks in both the black and white oak groups. They are generally more hardy than other oak trees and often live in very dry, sandy soil.
European OaksThe cork oak, Q. suber, grows in southern Europe. The holm oak, Q. ilex, also found in southern Europe, produces edible acorns Both are evergreen white oaks. The English oak, Q. robur, is a long-lived, deciduous white oak.
The Black Oak Group
The Black Oak group includes the remaining one-third of the oak species native to the United States. Except for a few species, the black oaks grow in the eastern two-thirds of the United States. All are deciduous, shedding their leaves in autumn. The leaves of most black oak species have bristles on the tips of the lobes. Lumber from the black oak group is called red oak wood because most of the wood from this group comes from the red oak. Among the most common species of the black oak group are:
Red OakThere are two species, the northern red oak and the southern red oak Both are important lumber species The northern red oak grows up to 90 feet (27 m) tall and is found from southern Canada to Georgia and west to Oklahoma. The leaves, 4 to 9 inches (10 to 23 cm) long, have shallow lobes and are tipped with bristles The acorns, from 1/2 to 1 1/8 inches (1.3 to 2.9 cm) long, are oval The southern red oak has deeply lobed leaver and small acorns, up to 1/2 inch (1.3 cm) long. It is found from New Jersey south to Florida and Texas.
The northern red oak is Q. rubra; the southern, Q. falcata.
Black Oak,the tallest oak tree, growing up to 125 feet (38 m) in height. Black oaks are found from Ontario to Florida and west to Texas. The leaves are 4 to 9 inches (10 to 23 cm) long, deeply lobed, and bristled. The acorns are oval and up to 1/2 inch (1.3 cm) long.
The black oak is Q. velutina.
Blackjack Oak,a small tree that grows up to 50 feet (15 m) tall. The leaves are narrow at the stem end and broaden out into three poorly defined, bristled lobes at the tar end. The acorns are oval and up to 1/4 inch (2 cm) long. This oak grows in poorer soil than do most tree oaks.
The blackjack oak is Q. marilandica.
Scarlet Oak,a tree that grows up to 80 feet (24 m) tall. The 3- to 7-inch (7.5- to 18-cm) leaves, bristled and deeply lobed, are darker on the upper side than on the lower. The acorns are oval and up to 1 inch (2.5 cm) long. This oak is prized for its brilliant scarlet fall coloring.
The scarlet oak is Q. coccinea.
Pin Oak,another oak prized for its fall coloring. The pin oak is a roughly cylindrical tree that grows up to 90 feet (27 m) tall. It has a heavy central trunk and small side branches. Its leaves, of medium size, are deeply lobed and bristled, and its acorns are small, about 1/2 inch (1.3 cm) long.
The pin oak is Q. palustris.
Willow Oak,an oak with distinctive yellow-green leaves shaped like a willow's. They are smooth-edged and unbristled and are about 4 inches (10 cm) long. The acorns, about 1/2 inch (1.3 cm) long, are rounded. This oak grows up to 80 feet (24 m) tail and is found rooted in heavy, damp clay from New Jersey south to Florida and Texas and north to Illinois.
The willow oak is Q. phelhs.