A distributive ‘50% rule’ determines floral initiation rates in the Brassicaceae

The spatio-temporal production of flowers is key to determining reproductive fitness in most flowering plants and yield in many crop species, but the mechanisms regulating this ‘reproductive architecture’ are poorly characterized. Here, we show that in members of the Brassicaceae, total flower number is largely independent of inflorescence number and that the proportion of flowers initiated on the secondary inflorescences represents ~50% of total floral production, irrespective of secondary inflorescence number. This ‘50% rule’ acts as a coordinating principle for reproductive development in Brassicaceae, and similar principles may operate in other species. Our findings suggest that inflorescences continue to compete with each other for a fixed pool of meristematic potential after their activation.