The flowers are reddish purple, 10–20 mm diameter, with six petals (occasionally five) and 12 stamens, and are clustered tightly in the axils of bracts or leaves; there are three different flower types, with the stamens and style of different lengths, short, medium or long; each flower type can only be pollinated by one of the other types, not the same type, thus ensuring cross-pollination between different plants. The flowers are visited by many types of insects, and can be characterized by a generalized pollination syndrome.