Quercus macrocarpa, Michx.
Bur Oak. Over-cup Oak. Mossy-cup Oak.
Habitat and Range.—Deep, rich soil; river valleys.
Nova Scotia to Manitoba, not attaining in this region the size of the white oak, nor covering as large areas.
Maine,—known only in the valleys of the middle Penobscot (Orono) and the Kennebec (Winslow, Waterville); Vermont,—lowlands about Lake Champlain, especially in Addison county, not common; Massachusetts,—valley of the Ware river (Worcester county), Stockbridge and towns south along the Housatonic river (Berkshire county); Rhode Island,—no station reported; Connecticut,—probably introduced in central and eastern sections, possibly native near the northern border.
South to Pennsylvania and Tennessee; west to Montana, Nebraska, Kansas, Indian territory, and Texas.
Habit.—A medium-sized tree, 40-60 feet high, with a trunk diameter of 1-3 feet; attaining great size in the Ohio and Mississippi river basins; trunk erect, branches often changing direction, ascending, save the lowest, which are often nearly horizontal; branchlets numerous, on the lowest branches often declined or drooping; head wide-spreading, rounded near the center, very rough in aspect; distinguished in summer by the luxuriance of the dark-green foliage and in autumn by the size of its acorns.
Bark.—Bark of trunk and branches ash-gray, but darker than that of the white oak, separating on old trees into rather firm, longitudinal ridges; bark of branches sometimes developed into conspicuous corky, wing-like layers; season's shoots yellowish-brown, minutely hairy, with numerous small, roundish, raised dots.
Winter Buds and Leaves.—Buds brown, 1/16 to ⅛ inch long, conical, scattered along the shoots and clustered at the enlarged tips. Leaves simple, alternate, 6-9 inches long, 3-4 inches broad, smooth and dark green above, lighter and downy beneath; outline obovate to oblong, varying from irregularly and deeply sinuate-lobed, especially near the center, to nearly entire, base wedge-shaped; stalk short; stipules linear, pubescent.
Inflorescence.—May. Sterile catkins 3-5 inches long; calyx mostly 5-parted, yellowish-green; divisions linear-oblong, more or less persistent; stamens 10; anthers yellow, glabrous: pistillate flowers sessile or short-stemmed; scales reddish; stigma red.