Most Paulownia species have pseudo-dichotomous branches whose terminal buds dry up after winter. P. fortunei is exceptional in that the terminal buds sometimes grow into new branches. In young trees representing juvenile phase the leaves are large with long petioles, serrate margin, opposite and sometimes whorled in arrangement. The inflorescence is a cyme of two to five flowers may be pedunculate or subsessile. They are produced in the axils of diminutive or smaller leaves in summer and autumn.
Flowers are pedicellate and articulate at the apical end.
The lobes are triangular, with the upper middle lobe slightly larger, and usually densely covered with haris. In some species, the hairs fall at anthesis. The corolla is big, purple to white, two-lipped with two lobes on the upper lip, and three elongated lobes on the lower lip. The campanulate corolla tube is usually curved forward 5 mm from the base, after which it enlarges gradually or abruptly. Near the limbs, the upper lip presses downwards and makes the corolla flat.