Sweet gum is a large tree with a long, cylindrical trunk, pyramidal crown, and corky wings on branches and twigs.
Leaves are alternate, simple, star-shaped, with 5 (sometimes 7) lobes, 3–6 inches wide, deeply lobed; margin toothed, tips long-pointed; leaves slightly aromatic when bruised.
Bark is brown to gray, very rough with deep grooves and narrow, slightly scaly ridges.
Twigs are reddish- or yellowish-brown becoming gray, aromatic, often with corky wings on second-year’s growth; pores raised, dark.
Flowers April–May, with male and female flowers on the same twig; male flowers greenish-yellow, on an upright stalk in several tight, rounded clusters; female flowers in a single, drooping, round cluster about ½ inch in diameter.
Fruit matures in September–October, persists through winter; light brown, globe-shaped, formed by the union of multiple individual fruits, hard, spiny due to numerous woody, hornlike projections, 1–1½ inches in diameter.
Similar species: One cultivated variety of sweet gum, L. styraciflua 'Rotundiloba', does not bear the spiny fruits that many people object to in a public landscape. Its leaves have rounded lobes. Although it produces small clusters of inconspicuous flowers in the spring, it does not (usually) set fruit.