 The leaves are alternate, petiolate, and vary in shape on a single plant, with larger, broader leaves at the base of the stem and smaller, narrower leaves higher up; the leaf margin is serrated.The flowers are produced in dense erect panicles, each flower with a narrow, deeply five-lobed corolla, 1–2 cm or more long), mostly purple, sometimes pale blue, white or pink.The fruit is a capsule containing numerous small seeds.