Figure 1. Heterostyly in primroses.

(A) Schematic diagrams of a long-styled (left) and short-styled flower (right) from a distylous species such as Primula vulgaris. When an insect enters a long-styled flower it would pick up pollen mainly on its head. If this insect then visits a short-styled flower, the stigma would pick up the pollen from the insect’s head. Meanwhile, the high stamens would deposit fresh pollen on to the insect’s abdomen for effective transfer to the stigmas of long-styled flowers. (B) Huu et al. identified CYP730A50 as a duplicated gene that alters style length in Primula flowers. Flowers without CYP730A50 (left) produce brassinosteroids, which cause the cells in the style to elongate and produce a long style. On the other hand, flowers with this gene (right) in the S-locus suppress the production of brassinosteroids, which leads to a short style.