Bur oak

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Bur oak acorn

Bur oak pistillate flowers

Bur oak leaves and acorn

Bur oak bark

Bur oak staminate cakins

Bur oak fruit

Bur oak acorns and leaves

Bur oak pistillate flowers

Bur oak leaves

Bur oak habit

Bur oak leaves

Bur oak buds

Bur oak in winter

Bur oak leaf scar and buds

Bur oak

Bur oak

Bur oak

Bur oak leaves

Morphology

Trunk

Short, 20-60 inches in diameter; crown broad; bark dark gray, ridges long and flat-topped or short and blocky; branches horizontal, angular, rugged; branch bark with corky ridges.

Twigs

Stiff, coarse; bark yellowish-brown or ashy-grey, usually woolly; leaf scars large, half-round, somewhat elevated; bundle scars 10 or more, scattered; buds egg-shaped, reddish-brown.

Leaves

Alternate, simple, deciduous, egg-shaped to oblong, often fiddle-shaped, 6-10 inches long, 2.4-6 inches wide, thick, leathery; upper surface dark green, shiny; lower surface pale, pubescent; margins unevenly 5-7-lobed; lobes rounded; terminal lobe largest; lateral lobes often with deep, opposite sinuses near mid-leaf; sometimes shallow-lobed to nearly entire on deep shade branches; base wedge-shaped to round; stalk stout, .4 to 1.2 inch long.

Flowers

Late April-May, with leaves; monoecious (male and female flowers on same tree); staminate in slender, drooping catkins 2.8 to 4+ inches long, on previous year's twigs; staminate flowers greenish-brown; stamens several; anthers yellow; pistillate flowers inconspicuous, sessile or short-stalked, in groups of 1-4, clustered at base of leaves; flowers globular, 1/12 to 1/10 inch in diameter, often reddish; calyx 4-6-lobed, downy; corolla absent; stigma 3-lobed.

Fruit

Autumn of first season; acorns 1-3, variable in size and shape, 1-seeded; sessile or short-stalked; cup hemispheric, often deep, 1 to 1.2 inch tall, 1.4 to 1.8 inch wide, enclosing 1.2 to 2/3 or more of nut; cup scales rough, closely appressed, gray-woolly; cup rim fringed, awns .2 to .4 inch long; nut broadly egg-shaped, .4 to 1.6 inch long and wide, brown, finely pubescent; outer end rounded; base flattened.

Ecology

Habitat

Stream banks, prairies, riparian slopes, bottom lands in west, upland slopes in east; usually on limestone or calcareous clay soils.

Distribution

East 2/3 of Kansas

Practical Information

Uses

Native Americans boiled the bark and took the liquid to treat cramps and diarrhea and boiled the inner bark and combined it with black earth to make a black dye. The bark was also used by some tribes to splint broken legs. The acorns were used as food, roasted or boiled, and were chopped up and cooked in soups and with meats. A number of Great Plains tribes leeched the acorns with basswood ashes to remove the bitter taste.

Additional Notes