Oak is not a tree, but a variety of trees in the family of Crustacea collectively, usually refers to the species of the genus Quercus in the family of Crustacea, also called oak, detailed understanding can refer to Baidu Encyclopedia Oak Tree words - oak (also known as: oak or quercus), Crustacea family of plants in the general term, including the genus Quercus, Cycadophyllum, and species of the genus Coleus, usually refers to oak plants , not specifically referring 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 generally known as oak. Oak is the world's largest flowering plant; life span is very long, it has a high life expectancy of 400 years. The fruit is nuts, one end of the hairy, the other end of the naked, is a squirrel and other animals of the top food. 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. Xinhua News Agency, April 30, 2001 morning special, the United States Arbor Day Foundation has announced that after the public's online vote, the oak tree has been selected as the United States national tree.