Willow oak

Trees , deciduous, to 30 m. Bark dark gray and smooth, becoming darker and irregularly fissured with age, inner bark light orange. Twigs reddish brown, 1-2 mm diam., glabrous. Terminal buds chestnut brown, ovoid, 2-4 mm, apex acute, glabrous. Leaves: petiole 2-4(-6) mm, glabrous, rarely sparsely hairy. Leaf blade linear to narrowly elliptic, usually widest near middle, 50-120 × 10-25 mm, base acute, margins entire with 1 apical awn, apex acute; surfaces abaxially pale green, glabrous, rarely softly pubescent, adaxially light green, glabrous. Acorns biennial; cup shallowly saucer-shaped, 3-6.5 mm high × 7.5-11 mm wide, covering 1/4-1/3 nut, outer surface puberulent, inner surface light brown, pubescent, scale tips tightly appressed, acute; nut ovoid to hemispheric, 8-12 × 6.5-10 mm, often striate, glabrate, scar diam. 4.5-6 mm.

Flowering spring. Of bottomland flood plains, also on stream banks, dunes, and terraces, and, occasionally, on poorly drained uplands; 0-400 m; Ala., Ark., Del., D.C., Fla., Ga., Ill., Ky., La., Md., Miss., Mo., N.J., N.Y., N.C., Okla., Pa., S.C., Tenn., Tex., Va.

Individual trees with leaves softly pubescent abaxially may be classified as Quercus phellos forma intonsa Fernald; however, such leaves are known to occur on second-flush shoots from twigs bearing typical leaves.

Quercus phellos reportedly hybridizes with Q . coccinea (W. W. Ashe 1894); with Q . ilicifolia (= Q . × giffordi Trelease) and Q . incana (E. J. Palmer 1948); and with Q . marilandica , Q . nigra , Q . pagoda (= Q . × ludoviciana Sargent), Q . palustris , Q . rubra , Q . shumardii , and Q . velutina . D. M. Hunt (1989) cited evidence of hybridization also with Q . hemisphaerica , Q . imbricaria , Q . laurifolia , and Q . pumila .