Sweetgum is a monoecious tree. It contains individual male and female flowers on the same individual tree. Male flowers pollinate female flowers. The flowers are unisexual and greenish in color.

The distinctive compound fruit is hard, dry, and globose, 25–40 mm (1–1+1⁄2 in) in diameter, composed of numerous (40–60) capsules.[14] Each capsule, containing one to two small seeds, has a pair of terminal spikes (for a total of 80–120 spikes). When the fruit opens and the seeds are released, each capsule is associated with a small hole (40–60 of these) in the compound fruit.

Fallen, spiky, opened fruits are often abundant beneath the trees; these have been popularly nicknamed "burr (or bir) balls", or "gum balls"