Oak, also known as oak or quercus. A general term for plants in the family Crustacea, including species of Quercus, Quercus serrata and Quercus serrata, usually refers to the genus Quercus, not specifically to a particular species of tree. The genus Quercus has 615 species, of which 450 are from the subgenus Quercus and 188 are from the subgenus Quercus glauca. Its fruit is called acorns, and the wood is known generically as oak.
The oak tree is the world's largest flowering plant; life span is very long, it has a high life expectancy of 400 years. The fruit is a nut, furry at one end and naked at the other, and is a fine food for animals such as squirrels. Research has found that a Jurupa oak tree in California has survived for at least 13,000 years and may be the world's oldest known living creature.
On April 30, 2001, the Arbor Day Foundation announced that the oak tree had been chosen as the national tree of the United States after a popular online vote.
Deciduous or evergreen trees, up to 25 to 30 meters high or more. Bark dark gray-brown, slightly smooth. Branchlets brown, glabrous. Winter buds long ovate, 3-5 mm long, glabrous, bud scales dark brown, numerous, imbricate. Leaf blade ovate or elliptic, 10-20 cm long, 7-10 cm wide, apically acuminate, base cuneate, leaf margin 5-7-pinnatipartite on each side, lobes finely dentate, leaf surface dark green, leaf abaxial surface light green, glabrous or with tufts of hairs in the vein axils; petiole 2.5-5 cm long, glabrous when old.
Staminate inflorescences open at the same time as the leaves, several clustered; female flowers solitary or 2~3 borne on a raceme ca. 1 cm long.
Shell cupular, enclosing 1/4-1/3 of nut, 1.5-1.8 cm in diam. and 1-1.2 cm in height; bracteoles triangular, densely imbricate, glabrous and shiny. Nut long ellipsoid, ca. 1.5 cm in diam. and 2-2.5 cm in height, light brown, thinly tomentose, gradually glabrescent; apical part rounded, with a stylopodium; umbilicus flat or slightly concave. Fruiting flat or slightly concave. Native to the Americas. This species is resistant to water and moisture. The nut contains 46.1% starch, 10.6% tannin, 12.6% oil, 7.4% protein.