Heterostyly (distyly) in the primrose (Primula)

Two or sometimes three flower morphs are present. Each morph can only fertilize the other. The two mating groups differ in style length, anther height, pollen size and number, and also in their incompatibility behaviour. In reasonably large populations the long-and the short morphs are equally frequent.

1 - Heterostyly (after Silvertown and Charlesworth 2001)