Distribution.—Massachusetts, Indiana, south to Florida, and west to Oklahoma and Texas. In Indiana it is confined to the southwestern part of the State. In our area it is found on the crest of ridges in the knob area where it is generally associated with black, and black jack oaks, hence in our poorest and thinnest soils. West of the knob area it takes up different habitats. From Vigo County southward it is found on sand ridges associated with black and black jack oaks. West of the knob area it is frequently found in black oak woods and in Warrick County about two miles southwest of Tennyson it is a frequent tree in the Little Pigeon Creek bottoms which are a hard light clay soil. Here it is associated with pin oak and cork elm (Ulmus alata). In the Lower Wabash Valley, especially in Point Township of Posey County in the hard clay of this area it is a frequent to a common tree, associated with Spanish, pin, swamp, white and shingle oaks, and sweet gum. In this area it grows to be a large tree.
This species has been reported for Hamilton County by Wilson, but I regard this reference a wrong identification which will relieve Hamilton County of the reputation of having "post oak" land. It was reported, also, by Gorby for Miami County. Since Gorby's list is wholly unreliable, it is best to drop this reference. Higley and Raddin[37] reported a single tree near Whiting. Nieuwland[38] reported this species from near Mineral Springs in Porter County, the report being based on his number 10,207 which I have not seen. There is no reason to doubt these references, because it is not an unusual thing to find a southern form jump from southern Indiana to a congenial habitat about Lake Michigan.
Remarks.—Wood is similar but tougher than white oak, and its uses are the same as white oak. Since in our area the tree is usually medium sized, most of the trees are worked up into crossties. A tree in a black oak woods 4 miles east of Washington in Daviess County measured 2.22 meters (871/2 inches) in circumference breast high. This species in some localities is called iron oak, and in Gibson County on the sand dune area it is called sand bur oak.
QUERCUS MACROCARPA Michaux. Bur Oak. (× 1/2.)
Acorns from different trees.
The right two belong to the variety OLIVÆFORMIS.
7. Quercus macrocàrpa Michaux. Bur Oak. [Plate 46.] Large trees; branchlets of young trees generally develop corky wings which are usually absent on mature trees; leaves on petioles 1-2 cm. long, obovate in outline, generally 1-2.5 dm. long, the margins more or less deeply cut so that there are usually 7 lobes, sometimes only 5, or as many as 9 or 11, sometimes the sinuses extend to the midrib, giving the leaf a "skeleton" appearance, the lobes are very irregular in shape and variously arranged, but often appear as if in pairs, lobes rounded and ascending, the larger lobes are sometimes somewhat lobed, the three terminal lobes are usually the largest and considered as a whole would equal in size one half or more of the entire leaf area, the base of the leaf is wedge-shape or narrowly rounded; leaves at maturity are dark green and smooth above, or somewhat pubescent along the midrib, a gray-green and woolly pubescent beneath; acorns usually solitary, sometimes in pairs or clusters of three, sessile or on short stalks, sometimes on stalks as long as 2.5 cm.; nuts very variable in size and shape, ovoid to oblong, often very much depressed at the apex, 2-3 cm. long, enclosed from 1/3 to almost their entire length in the cup which is fringed at the top; cups thick and large, sometimes 4.5 cm. in diameter; scales tomentose on the back and somewhat tuberculate, blunt near the base of the cup, but at and near the top of the cup they become long attenuate and on some trees appear almost bristle like; kernel sweet.