Quercus marilandica aka Blackjack Oak

Quercus marilandica, or blackjack oak, belongs to the beech family, Fagaceae. This deciduous tree grows across the central and eastern United States. Its range reaches from New York and Iowa to Florida and Texas. It grows on dry ridges, woodland edges, and poor soils. Some plants stay small and take a shrub form. Growth is slow, and the tree can live for many years.

Garden trees reach about 30–50 feet (9–15.2 metres) tall. Their crowns spread about 20–40 feet (6–12.2 metres) wide. Some sources describe smaller trees of 20–30 feet (6–9 metres). Rare trees reach 70–90 feet (21–27 metres). A short trunk bears thick, twisted limbs and a rounded crown. The dark bark splits into rough, near-square plates with age. Stout brown twigs have hairs, as do the pointed buds.

The thick, simple leaves grow in an alternate pattern. Their narrow bases widen toward three shallow, bristle-tipped lobes. Glossy green tops contrast with brownish hairs beneath. Fall leaves turn red, yellow, or brown. Some stay on the tree well into winter. Small yellow-green flowers appear in spring, with reports spanning March through June. Male flowers form catkins; female flowers grow in short spikes. Light brown acorns ripen in their second autumn. A scaly cup covers roughly half of each nut.

Give this oak full sun and soil that drains well. It also tolerates light shade, poor ground, and drought. Acid soil suits it best, though RHS also lists neutral soil. It grows in sand, loam, clay, and shallow rocky ground. Sources place it in USDA zones 6–9 and UK rating H6. It needs little upkeep and suits woodland or native plant areas. Nurseries seldom stock it, and its shape limits formal landscape use. Caterpillars feed on the tree, while birds and mammals eat acorns. Wildlife also uses it for nesting.

Possible pests include aphids, leaf miners, caterpillars, and gall wasps. Powdery mildew and honey fungus may also cause problems. People use its wood for charcoal, fuel, and fence posts. The seeds have food uses after tannin removal and cooking. Raw leaves and fruit can cause stomach pain and bowel problems. Dogs can also become ill after eating this plant. Treat its acorns as food only after proper processing.