Genetic basis for innovations in floral organ identity

Of the many innovations associated with the radiation of the angiosperms, the evolution of a petal identity program is among the best understood from a genetic standpoint. Although the existing data do indicate that similar genetic mechanisms control petal development across diverse taxa, there is also considerable evidence for variability in petal identity programs, likely due to a number of factors. These points are illustrated through a review of our current knowledge on the subject, integrating phylogenetic, morphological, and genetic studies. Comparative studies of petal identity highlight the complex nature of homology in plants and stand as a cautionary tale for the interpretation of gene expression data.