Quercus phellos aka Willow Oak

Willow oak, Quercus phellos, is a deciduous tree in the beech family, Fagaceae. It belongs to the red oak group. It grows wild across the central and eastern United States, from New York south to Florida. Its range runs west to Missouri and Texas. In the wild it favours woods beside swamps, streams and canals. The name phellos comes from a Greek word for cork.

In gardens it usually reaches 40 to 75 feet (12 to 23 m) tall and 25 to 50 feet (8 to 15 m) wide. Old wild trees can top 100 feet (30 m). Young trees have a pyramid shape. With age the crown becomes oval or broadly rounded. The tree grows fast, lives long and has a fine texture.

The leaves look more like a willow's than an oak's. They are narrow, lance-shaped and unlobed, about 2 to 5 inches (5 to 13 cm) long. Each has a smooth, wavy edge and a small bristle at the tip. They are glossy green above and paler beneath. In autumn they turn yellow, bronze or russet red, and the colour comes late. Young bark is smooth and reddish brown. Older bark turns grey-brown with shallow ridges and furrows. Slender, hairless twigs carry small, sharp, reddish-brown buds.

Male and female flowers appear on the same tree in spring, roughly March to May. The males hang in yellow-green catkins 2 to 3 inches (5 to 7.5 cm) long. The females are tiny and easy to miss. Small rounded acorns follow, about half an inch (1.3 cm) long, in shallow saucer-like cups. They take two seasons to ripen and drop in autumn. Trees start bearing acorns at around 15 to 20 years old.

Willow oak likes full sun or light shade and deep, moist, well-drained, acid soil. It copes with clay, sand and wet ground, and tolerates some drought. It also handles salt, heat and city pollution. Alkaline soil can yellow the leaves through iron shortage. A fibrous root system makes it easier to move than most oaks. It is hardy in USDA zones 5 to 9 and rated H6 in the UK. Planters use it as a shade tree for parks, large lawns and streets. It also suits pond edges. Turkeys, ducks, woodpeckers, squirrels and other mammals eat the acorns. The tree hosts many moth and butterfly caterpillars, including hairstreaks and the imperial moth.

Willow oak resists pests better than many oaks, but problems can occur. Possible insects include scale, borers, leaf miners, lace bugs, gall wasps and caterpillars such as the orange-striped oakworm. Diseases include root rot, cankers, anthracnose, oak wilt, leaf spots and powdery mildew. Strong winds can damage the branches.

The acorns are edible once boiling or soaking removes the bitter tannins. People have ground them into flour for bread or used them to thicken stews. The leaves contain tannins and are mildly poisonous. They pose a particular risk to horses and can harm dogs. Symptoms include stomach pain, constipation and later bloody diarrhoea.