Quercus macrocarpa aka Burr Oak

Bur oak, Quercus macrocarpa, is a large deciduous tree in the beech family, Fagaceae. It belongs to the white oak group. Other common names include burr oak, mossycup oak and moss-cap oak. It is native to central and eastern North America. Its range runs from Nova Scotia to Pennsylvania and west to Manitoba and Texas. It is a signature tree of the old Midwestern oak savannas.

In gardens it usually reaches 70 to 80 feet (21 to 24 metres) tall. Its spread often matches or exceeds its height. The RHS gives a top height of about 82 feet (25 metres). Young trees are somewhat columnar, but older trees develop a broad, rounded crown. A massive trunk carries short, stout branches. The tree has a coarse texture and lives a long time. Sources disagree on its pace: most call it slow, while one calls it fairly fast.

The bark is gray to gray-brown and becomes deeply furrowed with narrow, flat ridges. Young stems are stout and yellow-brown, and often develop corky ridges after their first year. The leaves are alternate, simple and leathery, from 4 to 12 inches (10 to 30 cm) long. They are dark green above and pale and hairy beneath. Deep rounded lobes cut nearly to the midrib, often splitting the leaf almost in two. Autumn colour is a dull yellow-brown.

Male and female flowers grow in separate catkins on the same tree. They open in spring as the leaves expand and have little garden value. The acorns ripen in a single season and fall in autumn. They measure up to 2 inches (5 cm) across. A deep, scaly cup with a shaggy fringe covers half or more of the nut. This fringe gives the tree its common names.

Bur oak needs full sun and suits only large lawns, parks and other open spaces. It grows in clay, loam, sand or chalk if drainage is good. It tolerates alkaline soil better than most oaks but dislikes very acid ground. It also copes with drought, poor rocky soil and urban conditions. A long taproot makes older trees hard to move. It is hardy to USDA zone 3 and rated H7 in the UK.

Planters use it as a shade tree, street tree or specimen, and in windbreaks and land reclamation. The strong wood goes into cabinets, barrels, flooring and fence posts. Deer, turkeys, squirrels and many other animals eat the acorns. Mature trees offer birds shelter and nest sites. The leaves feed caterpillars of hairstreak butterflies and the imperial moth.

The tree has no serious problems in most areas and needs little care. Possible diseases include oak wilt, powdery mildew, anthracnose and honey fungus. Pests include scale, leaf miners, gall wasps, lace bugs, borers and nut weevils. The acorns become edible once boiling or soaking removes their bitter tannins. Some trees bear sweet acorns, and cooks grind them into flour. Raw acorns can poison people, horses and dogs, causing stomach pain and diarrhoea.