A genus of two species of small deciduous trees, natives of China. Flowers on slender pedicels, arranged in short racemes terminating leafy branchlets. Ovary inferior (superior in Styrax). Calyx top-shaped, shortly five- to seven-lobed. Petals five to seven, united at the base (in the allied Halesia the corolla is four-lobed). Style slender, longer than the stamens. Fruits woody, not winged or ribbed.
The genus is named after J. G. Jack of the Arnold Arboretum, a Canadian by birth, who was concerned with Chinese botany and introduced several species from N. China and Korea early this century.