Variations on a theme: Changes in the floral ABCs in angiosperms

Angiosperms display a huge variety of floral forms. The development of the ABC-model for floral organ identity, almost 20 years ago, has created an excellent basis for comparative floral development (evo-devo) studies. These have resulted in an increasingly more detailed understanding of the molecular control circuitry of flower development, and the variations in this circuitry between species with different types of flowers. In this review, we analyze the variations in the molecular control of floral organ development: the changes in the floral ABCs. In addition, we discuss the control and diversification of inflorescence architecture, as this is another important source of structural diversity between flowering species.