This is an Australasian genus of few species, with the flowers in simple umbels, and the fruit very much flattened laterally. From rough, and a membrane or skin.

1. T. coerulea, better known as Didiscus caeruleus. - This is the only familiar ornamental annual species of this family. It grows from 1 to 2 feet high. Leaves triternately divided into linear segments. Flowers bright blue. Fruit tubercular.