SEPALLATA (SEP) genes form an integral part of models that outline the molecular basis of floral organ determination and are hypothesized to act as co-factors with ABCD floral homeotic genes in specifying different floral whorls. The four SEP genes in Arabidopsis function redundantly, but the extent to which SEP genes in other flowering plants function similarly is unknown. Using a recent 113-gene SEP phylogeny as a framework, we find surprising heterogeneity among SEP gene C-terminal motifs, mRNA expression patterns, protein-protein interactions and inferred function. Although some SEP genes appear to function redundantly, others have novel roles in fruit maturation, floral organ specification and plant architecture, and have played a major role in floral evolution of diverse plants.