Quercus suber

Cork Oak is a medium to large size attractive broadleaf evergreen shade tree that grows 70 to 100 feet tall and equally as wide. It has a short trunk, thick branches, and a rounded crown. Corky bark covers the trunk and major limbs of the tree. The spongy bark of mature trees is used to make wine bottle corks, cork flooring, and other items. The cork is harvested when the tree reaches 30 to 40 years of age and then every 9-11 years for up to 12 times within its lifetime. 

It is native to western Africa and southwestern Europe and is found in forests and open woodlands. The Cork Oak is the National Tree of Portugal where half of the world's commercial cork is produced. There are plantations in some European and African countries especially Portugal and Spain that commercially grow the cork oak tree.

The genus name, Quercus, is the Latin name for oak trees. The epithet name, suber, is Latin and is similar to the Greek word syphar which means "a piece of old skin" or "a piece of wrinkled skin."

The cork oak is best grown in acidic, well-drained, moist to dry soils in full sun to partial shade. It is low maintenance, deer resistant, and drought tolerant.  Because of the high levels of tannins in the leaves, bark, and acorns, oaks are toxic to horses.

The cork oak bark is light gray and thick, with reddish-brown furrows. The leaves of this tree are elliptic to ovate with wavy margins, leathery, sparsely toothed, and shiny dark green on the upper surface. The undersides are white with grayish hairs. Appearing in the spring, the male flowers are inconspicuous yellow-greenish catkins, and the female flowers are short clusters. The female flowers produced long, narrow acorns with a shaggy cap that are harvested in the fall.

The world's largest Cork Oak tree is in a small village in Portugal and was planted in 1783. The tree is known as Sobreiro Monumental or Whistler's Tree and is over 230 years old. The tree is 53 feet tall and 14 feet in diameter. Its cork has been collected over 20 times. In 1991, the tree produced 2646 pounds of raw cork which is enough cork to stopper 100,000 wine bottles.

In the United States, it can be grown in warmer winter areas and makes an attractive shade tree.

It is a host plant for the larvae of the Imperial moth (Eacles imperialis), as well as numerous butterflies, including Banded hairstreak (Satyrium calanus), Edward's hairstreak (Satyrium edwardsii), Gray hairstreak (Strymon melinus), White-m hairstreak (Parrhasius malbum), Horace's duskywing (Erynnis horatius), and Juvenalis duskywing (Erynnis juvenalis).

Seasons of Interest:

Bark:  Winter     Foliage:  Spring, Summer, Fall, and Winter     Fruits:  Fall

Quick ID Hints: 

• light gray bark with reddish-brown furrows, thick layers of cork
• light gray-brown stems, gray fuzz, reddish-brown buds, triangular and pointed
•  alternate, simple, leathery, ovate to elliptical dark green leaves, undersides are whitish and fuzzy, margins are sparsely toothed and wavy
• yellow-greenish, 2-to-3-inch chainlike, male catkin flowers and small clusters of female flowers
• fruit is a 1 to 1.5-inch long, narrow acorn with a scaly cap

Insects, Diseases, and Other Plant Problems: Insects that may potentially be troublesome include scales, oak skeletonizer, leaf miner, galls, oak lace bugs borers, caterpillars, orangestriped oakworm, buck moth, whitemarked tussock moth, and nut weevils.  Oaks are susceptible to many diseases including oak wilt, chestnut blight, shoestring root rot, anthracnose, oak leaf blister, cankers, leaf spots, and powdery mildew. 

The Clemson Cooperative Extension Home and Garden Information Center has a factsheet on common pests and insects. 

VIDEO created by Ryan Contreras for “Landscape Plant Materials I:  Deciduous Hardwoods and Conifers or Landscape Plant Materials II:  Spring Flowering Trees and Shrubs” a plant identification course offered by the Department of Horticulture at Oregon State University