Quercus acutissima aka Sawtooth Oak

Sawtooth oak, Quercus acutissima, is a deciduous tree in the beech family, Fagaceae. Its wild range runs from the Himalaya through China and Indo-China to Korea and central and southern Japan. It belongs to the Cerris group, which sits between the red and white oaks. It reached North America in 1862. Other common names include sawthorn oak and Japanese silkworm oak.

In gardens it grows 40 to 60 feet (12 to 18 m) tall. The spread is about 30 to 50 feet (9 to 15 m). Young trees have a pyramidal outline. With age the crown becomes oval to broadly rounded and wide. Growth is moderate, though one source calls it fast.

The bark is gray to black. It develops corky ridges and furrows as the tree ages. Twigs are slender, smooth and red to gray-brown. The leaves are glossy, dark green and lance-shaped, about 4 to 7.5 inches (10 to 19 cm) long. Parallel veins end in bristle-tipped teeth along the margin. This saw-like edge gives the tree its name. Autumn colour is yellow to copper brown. Dead leaves often cling to the branches through winter.

Small yellowish-green flowers appear with the new leaves in spring, often in May. Male and female flowers form in separate catkins on the same tree. The male catkins hang down and look golden. Oval acorns follow, about 1 inch (2.5 cm) long. A spiny, scaly cup covers about two-thirds of each nut and looks like a bird's nest. Trees may crop from about ten years old. Mature trees drop heavy loads of acorns and cups, which makes a messy litter.

The tree does best in full sun and moist, rich, well-drained, acidic soil. It adapts to many soils and tolerates drought, heat, humidity and wind. It is hardy in USDA zones 5 to 9. Young trees may suffer in the coldest parts of that range. In neutral or alkaline soil, leaf yellowing (chlorosis) is common and can harm the tree badly. It makes a shade tree for large lawns and parks. Oaks host many moth and butterfly caterpillars, including hairstreaks and the imperial moth.

Sawtooth oak has few serious pest problems. Possible insects include scale, leaf miners, oak lace bugs, borers, caterpillars and nut weevils. Oak diseases such as oak wilt, anthracnose, cankers, leaf spots and powdery mildew can also strike. The tree now spreads into forests in the eastern United States. Some states treat it as invasive, and Wisconsin bans it. Extension experts advise planting native oaks instead.

The acorns contain bitter tannins. Leaching or boiling removes them, and the nuts can then be eaten or ground into flour. Raw acorns carry low-severity toxicity. They may cause stomach pain, diarrhoea and gut blockage, and they pose a problem for horses. Traditional medicine used the astringent bark, seed cups and seeds. The wood serves for building, fuel and charcoal, and the cups yield a black dye.