Large trees to shrubs, with simple, alternate, deciduous or evergreen, entire to deeply lobed leaves. The leaves are rather thick and woody, and remain on the tree either all winter or at least until nearly all other deciduous leaves have fallen. Flowers insignificant; the staminate ones in catkins; blooming in spring. Fruit an acorn, which in the White, Chestnut, and Live Oaks matures the same year the blossoms appear; while in the Red, Black, and Willow Oaks the acorns mature the second year. They remain on the tree until late in autumn. The Oaks, because of their large tap-roots, can be transplanted only when small. Most of the species are in cultivation. The species are very closely related, and a number of them quite readily hybridize; this is especially true of those of a particular group, as the White Oaks, Black Oaks, etc.

There is no attempt in the Key to characterize the hybrids, of which some are quite extensively distributed. Quercus heterophylla, Michx. (Bartram's Oak), supposed to be a hybrid between Quercus Phellos and Quercus rubra, is found quite frequently from Staten Island southward to North Carolina.

* Cultivated Oaks from the Old World; bark rough; leaves more or less sinuated or lobed. (A.)
A. Acorn cup not bristly 20.
A. Acorn cup more or less bristly 21.
* Wild species, occasionally cultivated. (B.)
B. Leaves entire or almost entire, or merely 3- (rarely 5-) lobed at the enlarged summit. (C.)
C. Ends about equal, petioles very short. (D.)
D. Leaves small (2 to 4 in. long), evergreen, bark smooth, black (Live-oaks) 10.
D. Leaves not evergreen in the North, somewhat awned when young, bark very smooth, black and never cracked (Willow-oaks). (E.)
E. Down on the under side quite persistent 18.
E. Under side soon smooth 19.
C. Widened near the tip, somewhat obovate and the end usually 3-lobed; bark quite black, smooth or furrowed, but never scaly (Black-oaks). (F.)
F. Leaves acute at base16.
F. Leaves abrupt or cordate at base 17.
B. Leaves distinctly straight-veined, sinuate rather than lobed, the teeth generally rounded and never awned; bark white, rough and scaling (Chestnut-oaks). (G.)
G. Lobes rounded 5, 6, 7.
G. Lobes rather acute 8, 9.
B. Leaves coarsely lobed, the lobes usually rounded, never awned; bark white or whitish-brown, cracking and scaling off in thin laminæ (White Oaks). (H.)
H. Leaves crowded at the ends of the branchlets 4.
H. Leaves not crowded 1, 2, 3.
B. Leaves more or less lobed, the lobes and teeth acute and bristle-pointed; petiole slender; base rather abrupt; bark dark-colored, smooth or furrowed, but never scaly (Red Oaks). (I.)
I. Leaves smooth both sides, at least when mature 11, 12, 13.
I. Leaves soft-downy beneath 14, 15.

Q. álba.

1. Quércus álba, L. (American White Oak.) Leaves short-stemmed, acute at base, with 3 to 9 oblong, obtuse, usually entire, oblique lobes, very persistent, many remaining on the tree through the winter; pubescent when young, soon smooth, bright green above. Acorns in the axils of the leaves of the year, ovoid-oblong, 1 in., in a shallow, rough cup, often sweet and edible. A large tree, 60 to 80 ft. high, with stem often 6 ft. in diameter; wood light-colored, hard, tough and very useful. Common throughout.

Q. stellàta

2. Quércus stelláta, Wang. (Post-oak. Rough or Box White Oak.) Leaves 4 to 6 in. long, sinuately cut into 5 to 7 roundish, divergent lobes, the upper ones much larger and often 1- to 3-notched, grayish-or yellowish-downy beneath, and pale and rough above. Acorn ovoid, about ½ in. long, one third to one half inclosed in a deep, saucer-shaped cup; in the axils of the leaves of the year. A medium-sized tree, 40 to 50 ft. high, with very hard, durable wood, resembling that of the White Oak. Massachusetts, south and west.