tanbark oak, (Notholithocarpus densiflorus), evergreen tree of the beech family (Fagaceae), native to coastal areas of southern Oregon and northern California. The plant is related to true oaks (Quercus) and is noted for its tannin-rich bark. The tanbark oak is cultivated as an ornamental in cooler regions of the temperate zone. Its hard, light brown, red-tinged wood is used for agricultural implements and furniture. The bark chips are used in tanning leather and as a mulch.
The tanbark oak is usually about 20 metres (65 feet) tall but occasionally reaches 45 metres (148 feet); it becomes shrubby at high elevations. It has horizontal spreading limbs that form a dense, symmetrical, rounded crown. The short-pointed, alternate, leathery leaves may be toothed or slightly scalloped, with the margins rolled under. They are pale green above and have a brownish crusty coat of matted hairs below; the undersides become bluish white as the hairs are shed during the summer.
The flowers of the tanbark oak resemble those of the chestnut (Castanea), but the fruit is similar to an oak’s acorn in appearance. Most male flowers are borne in long erect catkins, and female flowers are usually in clusters at the base of the male catkins. The fruit, a single nut, is held in a scaly burrlike cup.
The plant was formerly placed with the Asian stone oaks of the genus Lithocarpus, but phylogenetic evidence led to a revision of its taxonomy. Tanbark oak is the only species of the genus Notholithocarpus.