General: Beech Family (Fagaceae). Native trees commonly growing to 15–20 m, sometimes to 30 m, the lateral branches relatively persistent (slow in self-pruning), with an open, irregularly shaped crown; bark dark gray, scaly or flat-ridged, often peeling off in large, ragged, papery curls. Leaves are deciduous, alternate, obovate to narrowly elliptic or narrowly obovate, (8–)12–18(–21) cm long, (4–)7–11(–16) cm wide, usually with regularly spaced, shallow, rounded teeth, or toothed in distal half only, or moderately to deeply lobed, upper surfaces dark green and glossy, lower surfaces lighter green to whitish, softly hairy. Male and female flowers are borne in separate catkins on the same tree (the species monoecious) on the current year's branchlets. Acorns maturing the first year, ovoid-ellipsoid or oblong, mostly 1.5–3 cm long, single or clustered in groups of 2–4, on a stalk (peduncle) 3-8 cm long; cup enclosing 1/3–1/2 of the acorn, scales closely appressed, finely grayish tomentose, those near rim of cup often with a short, stout, irregularly recurved spinose tip. The common name is from its typical habitat and its membership in the white oak subgroup.

Swamp white oak is a member of the white oak subgroup (subgenus Quercus) and hybridizes with related species, including white oak (Q. alba), overcup oak (Q. lyrata), and bur oak (Q. macrocarpa). Swamp white oak is distinguished from all similar native species by its long-stalked acorns.

Variation within the species: Formal variants are not recognized.