The Japanese emperor oak (Quercus dentata), also called a sweet oak or Korean oak, is a slow growing medium to tall tree that typically is 50-65 feet tall when mature. It is native to Japan, China and Korea, was introduced into Europe in the beginning of the 19th century,nd brought to the United States in 1862. The leaves are rather large and have shallow lobed margin and are hairy underneath. They stay on the tree during the winter. Bark is tan. The small acorns have distinct bushy copper colored caps. Japanese oak is extremely rare.