Trees , deciduous or tardily deciduous, to 30 m. Bark grayish black, fissures irregular, shallow, inner bark pinkish. Twigs dark red-brown, 1.5-2.5 mm diam., glabrous. Terminal buds reddish brown, ovoid, 3-6.5 mm, puberulent throughout, occasionally densely pubescent on apical 2/3. Leaves: petiole 2-9 mm, glabrous. Leaf blade distinctly obtrullate, rarely elliptic or merely obovate, widest near apex, 30-120(-160) × 15-60(-70) mm, base attenuate or cuneate, rarely rounded, margins entire with 1 apical awn or with 2-3 shallow lobes and 2-5 awns (leaves on juvenile or 2d-flush growth may be deeply lobed with more awns), apex obtuse to blunt or rounded; surfaces abaxially glabrous except for minute or conspicuous axillary tufts of tomentum, veins rarely raised, adaxially glabrous with secondary veins somewhat impressed. Acorns biennial; cup saucer-shaped, 2.5-5.5 mm high × 10-18 mm wide, covering 1/4 nut or less, outer surface puberulent, inner surface sparsely to uniformly pubescent, scale tips tightly appressed, acute; nut broadly ovoid, 9.5-14 × 9.5-14.5 mm, often faintly striate, glabrate, scar diam. 6-11.5 mm. Flowering spring. Mesic alluvial and lowland sites, also barrens, dunes, hammocks, and low ridges to steep slopes; 0-450 m; Ala., Ark., Del., Fla., Ga., Ky., La., Md., Miss., Mo., N.J., N.C., Okla., S.C., Tenn., Tex., Va. Typically on mesic alluvial and lowland sites, Quercus nigra also occurs on a wide variety of soil types and in a diversity of habitats. Trees with 3-lobed leaves with attenuate bases have been recognized as Quercus nigra var. tridentifera Sargent.

Quercus nigra reportedly hybridizes with Q . falcata (= Q . × garlandensis E. J. Palmer), Q . incana , Q . laevis (= Q . × walteriana Ashe), Q . marilandica (= Q . × sterilis Trelease), Q . phellos (= Q . × capesii W. Wolf), Q . shumardii (= Q . × neopalmeri Sudworth), and Q . velutina ( Q . × demarei Ashe). In addition, D. M. Hunt (1989) cited evidence of hybridization also with Q . arkansana , Q . georgiana , Q . hemisphaerica , Q . laurifolia , Q . myrtifolia , Q . palustris , Q . rubra , and Q . texana.