Var. tinctòria, Gray. (Quercitron, Yellow-barked, or Black Oak.) Leaves with broader undivided lobes, commonly paler and somewhat pubescent beneath, turning brownish, orange, or dull red in autumn; cup-scales large and loosely imbricated or squarrose when dry, yellowish gray, pubescent; bark of trunk darker-colored and rougher on the surface, thicker, and internally orange, much more valuable for the tanner and dyer; buds longer and more pointed; cup sometimes less top-shaped. (Q. tinctoria, Bartram.)—Dry or gravelly uplands, S. Maine to S. Minn., E. Neb. and Tex. Intermediate forms connect this with the type. The bark is largely used in tanning.
Var. ambígua, Gray. (Gray Oak.) Found along our northeastern borders to Lake Champlain and northward, figured and briefly characterized by Michaux as with the foliage of Q. rubra and the fruit of Q. coccinea. It was considered by Dr. Engelmann as a form of Q. rubra with cups hemispherical or even turbinate.
13. Q. palústris, Du Roi. (Swamp Spanish or Pin Oak.) Cup flat-saucer-shaped, sometimes contracted into a short scaly base or stalk, fine-scaled (5–7´´ broad), very much shorter than the usually globose or depressed acorn, which is 5–7´´ long; leaves deeply pinnatifid with divergent lobes and broad rounded sinuses.—Low grounds; rather common, from Mass. to Del. and Md., west to Minn., E. Kan., and Ark.
[+][+] Mature leaves soft-downy beneath; cup saucer-shaped, with a somewhat top-shaped base, about half the length of the fully developed small acorn.
14. Q. falcàta, Michx. (Spanish Oak.) Leaves grayish-downy or fulvous underneath, obtuse or rounded at base, 3–5-lobed above (sometimes entire); the lobes prolonged, mostly narrow and more or less scythe-shaped, especially the terminal one, entire or sparingly cut-toothed; acorn globose, 4–5´´ long.—Dry or sandy soil, Long Island to Fla., and from S. Ind. to Mo. and Tex. A large or small tree, extremely variable in foliage; bark excellent for tanning.
15. Q. ilicifòlia, Wang. (Bear or Black Scrub-Oak.) Dwarf (3–8° high), straggling; leaves (2–4´ long) thickish, obovate, wedge-shaped at base, angularly about 5- (3–7-) lobed, white-downy beneath; lobes short and triangular, spreading; acorn ovoid, globular, 5–6´´ long.—Sandy barrens and rocky hills, N. Eng. to Ohio and Ky.
[*][*] Leaves entire or with a few teeth (or somewhat 3–5-lobed at the summit), coriaceous, commonly bristle-pointed; acorns globular, small (not over 6´´ long).
[+] Leaves thick, widening or often much dilated upward and more or less sinuate or somewhat 3–5-lobed; acorns globular-ovoid.
16. Q. aquática, Walter. (Water-Oak.) Leaves glabrous and shining, obovate-spatulate or narrowly wedge-form, with a long tapering base and an often obscurely 3-lobed summit, varying to oblanceolate; cup saucer-shaped or hemispherical.—Wet grounds, around ponds, etc., Del. to the Gulf, and from Ky. and Mo. to Tex.—Tree 30–40° high; running into many varieties, especially southward; the leaves on seedlings and strong shoots often incised or sinuate-pinnatifid; then mostly bristle-pointed.
17. Q. nìgra, L. (Black-Jack or Barren Oak.) Leaves broadly wedge-shaped, but sometimes rounded or obscurely cordate at the base, widely dilated and somewhat 3-lobed (rarely 5-lobed) at the summit, occasionally with one or two lateral conspicuously bristle-tipped lobes or teeth, rusty-pubescent beneath, shining above, large (4–9´ long); cup top-shaped, coarse-scaly; acorn short-ovoid.—Dry sandy barrens, or heavy clay soil, Long Island to S. Minn., E. Neb., and southward. A small tree (sometimes 30–40° high), of little value.