Bur Oak (Quercus Macrocarpa)

Bur Oak (Quercus Macrocarpa)

Beech Family: Fagaceae

Description: This native tree is 80-120' tall at maturity, forming an ovoid to globoid crown with a tall stout trunk (up to 5' across). The branches of the crown are ascending to widely spreading and somewhat crooked. The thick trunk bark is gray to gray-brown with flat corky ridges and deep irregular furrows. The bark of branches and twigs is gray-brown to brown and often rather corky with flat elevated ridges. Alternate leaves about 4-10" long and 2½–5" across develop from the twigs. These leaves are obovate or broadly elliptic in outline and pinnatifid with rounded lobes. Most lobes extend moderately to deeply into the leaf blade. The deepest lobes usually occur along the lower one-half of the blade. Leaf margins are undulate and irregular, lacking any bristles or true teeth. Upper leaf surfaces are dark green and glabrous, while lower surfaces are pale gray-green and densely tomentose with short fine hairs. These hairs are often stellate or clustered together (visible with a 10x hand lens). The petioles are ½–1" long, light green, and either glabrous or tomentose.

Bur Oak is monoecious, producing both male (staminate) and female (pistillate) flowers on the same tree. The male flowers are produced in drooping yellowish catkins about 2-5" long; individual male flowers consist of a lobed calyx with 5-20 stamens. Female flowers are either solitary or clustered together in groups of 2-3. Individual female flowers (about 1/8" in length) consist of a pistil that is covered with appressed scales (involucral bracts) with red styles at its tip. Overall, a female flower has the appearance of a tiny narrow cone. Both male and female flowers bloom as the leaves begin to develop during the spring. Cross-pollination is by wind. During the summer, fertile female flowers develop into nuts that are either solitary or occur in pairs. The nuts occur on short stalks up to 1" long (shorter than the petioles of the leaves); they are often nearly sessile. Nuts mature in a single year and usually germinate during the fall of the same year. Individual nuts (including their cups) are 1½–2½" long and similarly across; they are initially green, but become brown to grayish brown at maturity. The distinctive cups extend at least one-half the length of the nuts, sometimes nearly enclosing them. The coarse scales of the cups are keeled and rather knobby in appearance; the outer scales along the rim each cup have soft awns up to 1/3" (10 mm.) in length, forming a conspicuous fringe around the nut. The starchy meat of the nuts is low in tannins and potentially edible. The root system produces a deep taproot and widely spreading lateral roots. At favorable sites, this tree sometimes forms colonies.

Range and Habitat: Bur Oak is a common tree that is found in every county of Illinois. Habitats include moist bottomland woodlands, upland woodlands, and savannas where deciduous trees are dominant. This tree is most commonly found in bottomland woodlands a little outside of the flood zone. It also occurs in savannas and can be an invader of prairies because of its resistance to fire. Occasionally, Bur Oak is cultivated as a landscape tree, where it can become quite large.

Facebook - All About Illinois