Close, yet separate: patterns of male and female floral development in monoecious species

Much of our knowledge on flower development comes from hermaphroditic model species such as Arabidopsis, rice, petunia and snapdragon, whose perfect (bisexual) flowers bear both stamens and pistils. Indeed, most higher-plants are hermaphrodites, producing bisexual flowers in each individual. However, many plant taxa have evolved mechanisms to separate male and female reproductive functions, either within the same plant (monoecious plants) or on separate male and female individuals (dioecious plants). Dioecious plants have evolved genetic mechanisms for sex determination at the individual plant level. Here we turn our attention to monoecious plants, where sex determination mechanisms operate, in a temporally and spatially regulated pattern, within the same plant. We shall approach this developmentally fascinating phenomenon from two main angles. From an ecological/evolutionary viewpoint, we can try to evaluate the costs and benefits of such reproductive strategy. Several species, mostly wild plants, have been the focus of this type of study and have provided exciting insights on sex determination in plants. I will not attempt to comprehensively review such studies, but rather will give a few selected examples. Typically, they raise questions such as:‘Why should some plants be monoecious?’‘How did monoecy evolve?’‘What are the consequences for plant fitness?’The second approach deals with the production of sex organs in the flowers; monoecious plants pose several intriguing developmental questions that can be answered using genetic and molecular tools. Here, the underlying question is ‘How is a unisexual flower …