Dioecy has evolved independently several times during the evolution of flowering plants, but knowledge of the mechanisms involved is poor. Phoenix dactylifera is a dioecious species displaying strong dimorphism between pistillate and staminate flowers, and Daher et al. (pp. 255–266) describe the transition of reproductive buds from a bisexual to a unisexual stage. They find that unisexuality of date palm flowers results from cell cycle arrest of sterile sex organs, rather than from cell death.