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 oakThe 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.