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.

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Silver Maple (Acer Sacharinum)

 Silver Maple (Acer Sacharinum)

Maple Family: Aceraceae

Description: This tree is 60-100' tall at maturity, forming a short broad trunk and an ovoid to obovoid crown that is defined by long ascending branches of considerable size. Trunk bark of mature trees is gray and rough-textured, consisting of flattened scales and straight to curving furrows. On very old trees, the bark may become slightly shaggy when the scales become curved and somewhat loose. Trunk bark of young trees and branch bark are light gray and more smooth, while twigs are reddish brown, smooth, and covered with scattered white lenticels. Pairs of opposite deciduous leaves occur along the twigs and smaller branches. Individual leaves are up to 6" long and 4" across; they are palmately divided into 5 primary lobes. The primary lobes themselves are often divided into shallow secondary lobes and their margins have a few large teeth. All of the lobes are sharply cleft and pointed at their tips; the primary lobes extend deeply into the interior of each leaf. The upper leaf surface is light to medium-light green and glabrous, while the lower surface is conspicuously whitened and glabrous to mostly glabrous (some hairs may occur along the undersides of the major veins). The slender petioles of the leaves are up to 5" long, light green to red, and glabrous.

Individual trees of Silver Maple can be monoecious or dioecious; trees with perfect florets are rare. Some trees are capable of changing their gender from year to year. Staminate florets occur in small dense clusters about 1/3" across on short lateral spur-twigs; these florets are nearly sessile and they vary in color from yellowish green to red. Individual staminate florets consist of 4 sepals, 4-6 stamens, and no petals. At the base of each staminate cluster, there are several scaly bractlets. Pistillate florets also occur in small dense clusters about 1/3" across on very short peduncles; these florets are nearly sessile and they vary in color from greenish yellow to red. Individual pistillate florets consist of 4 sepals, a pistil with a pair of styles, and no petals. At the base of each pistillate cluster, there are several scaly bractlets. The blooming period occurs from early to mid-spring before the leaves develop. The florets are cross-pollinated by the wind. Fertile female florets soon develop pairs of samaras (seeds with elongated wings). In each pair, the samaras are held about 90° apart from each other (or a little less) and they are joined together at the base. At maturity, individual samaras are 1½-2½" long, becoming light brown; they dangle from slender pedicels and fall to the ground during early summer. The root system produces woody lateral roots that are fairly shallow and widely spreading. The leaves usually become pale yellow during the fall.

Range and Habitat: In Illinois, Silver Maple is a common tree that is found in every county. Habitats consist primarily of moist floodplain woodlands, riverbanks, and swamps. In these types of habitats, Silver Maple is often one of the codominant trees. In drier locations, it is not competitive with Sugar Maple (Acer saccharum) and other trees in the long run because its seedlings are less tolerant of shade. This tree is often cultivated as a landscape plant in yards and parks. In urban and suburban areas, the offspring of these cultivated trees often escape into adjacent areas that are not mowed (e.g., fence rows and vacant lots).