Bark: Light brown or dark brown, scarcely furrowed.
Twigs: Slender, smooth, reddish-brown to dark gray; pith star-shaped in cross-section; leaf scars alternate but crowded near the tip, half-round, usually slightly elevated, with several bundle traces.
Buds: Pointed, reddish-brown or dark gray, smooth, up to ⅛ inch long.
Leaves: Alternate, simple; blades divided more than half-way to the middle into 5-7 bristle-tipped lobes, dark green, shiny and more or less smooth on the upper surface, paler and with tufts of hairs along the veins on the lower surface, up to 7 inches long and 4 inches broad; leafstalk up to 2 inches long, slender, usually smooth.
Flowers: Staminate and pistillate borne separately, but on the same tree, appearing when the leaves begin to unfold, minute, without petals, the staminate in slender, drooping catkins, the pistillate in groups of 1-3.
Fruit: Acorns 1-4 together, with or without stalks, the nut hemispherical, up to ½ inch across, pale brown, frequently with darker lines, enclosed less than ¼ by the cup, the cup thin, saucer-shaped, reddish-brown, finely hairy.
Wood: Hard, heavy, coarse-grained, pale brown.
Uses: General construction, fuel, fence posts, ornamental.
Habitat: Moist soil; in floodplain woods; along streams; edges of swamps and ponds.
Range: Massachusetts across to southeastern Iowa, south to northeastern Oklahoma, east to northern Virginia.
Distinguishing Features: Pin Oak is recognized by its drooping lower branches and its small acorns.
WILLOW OAK Quercus phellos L.
Growth Form: Medium tree to 75 feet tall; trunk diameter up to 3 feet; crown narrowly round-topped.
Bark: Reddish-brown, smooth at first, becoming irregularly and shallowly furrowed with age.
Twigs: Slender, smooth, reddish-brown; pith star-shaped in cross-section; leaf scars alternate but crowded near the tip of the twigs, half-round, slightly elevated, with several bundle traces.
Buds: Ovoid, pointed, smooth, up to ⅛ inch long.
Leaves: Alternate, simple; blades without lobes or teeth, narrowly lanceolate to narrowly oblong, with a bristle tip, narrowed to the base, up to 5 inches long, up to 1 inch broad, light green and smooth on the upper surface, usually smooth and paler on the lower surface; leafstalks up to ½ inch long, smooth or slightly hairy.
Flowers: Staminate and pistillate borne separately, but on the same tree, appearing as the leaves begin to unfold, minute, without petals, the staminate in slender, drooping catkins, the pistillate few in a cluster.
Fruit: Acorns solitary or 2 together, with or without a short stalk, the nut more or less spherical, pale yellow-brown, enclosed less than ¼ its length by the cup, the cup reddish-brown, finely hairy.
Wood: Heavy, rather soft, strong, coarse-grained, pale reddish-brown.
Use: General construction.
Habitat: Swampy woods.
Range: New York across to southern Illinois and eastern Oklahoma, south to Texas, east to Florida.
Distinguishing Features: This and the Shingle Oak are the only oaks in Illinois with unlobed, untoothed leaves. The leaves of the Willow Oak are usually much narrower than those of the Shingle Oak.
ROCK CHESTNUT OAK Quercus prinus L.
Other Name: Chestnut Oak.
Growth Form: Medium tree up to 55 feet tall; trunk diameter up to 2½ feet; crown broad but irregular.
Bark: Dark brown, with conspicuous furrows between the rounded ridges.
Forest Trees of Illinois (third Edition) · The Wunder Library — complete classics, free to read, with narration.