The architecture of a flower is tightly linked to the way a plant pollinates, making it one of the most physiologically and ecologically important traits of angiosperms. Floral organ development is proposed to be governed by the activity of three different classes of organ identity genes (the ABC model), and the expression of those genes are regulated by a number of meristem identity genes. Here we use a transgenetic strategy to elucidate the role of one floral meristem identity gene, LEAFY (LFY), in the evolution of floral organogenesis of a self pollinator Idahoa scapigera and a obligatory out-crosser Leavenworthia crassa in the mustard family, Brassicaceae. By introducing the LFY genes from these two types of pollination habit into the genetic model species Arabidopsis thaliana, we provide evidence that changes in LFY influenced flower architecture probably by controlling the downstream organ identity genes.