Perennial herbs, with annual stems, which are simple and erect; latex milky. Leaves opposite or rarely whorled, usually narrowly linear. Flowers in fascicles. Calyx shorter than corolla. Corolla campanulate; lobes elliptic, spreading or reflexed, usually pilose on the back. Corona with lobes alternating with corolla lobes, each a dorsal outgrowth from the opposing stamen. Anthers 2-locular. Seeds many.