Controlled spatiotemporal cell division and expansion are responsible for floral bilateral symmetry. Genetic studies have pointed to class IITCPgenes as major regulators of cell division and floral patterning in model core eudicots. Here we study their evolution in perianth-bearing Piperales and their expression inAristolochia, a rare occurrence of bilateral perianth outside eudicots and monocots. The evolution of class IITCPgenes reveals single-copyCYCLOIDEA-likegenes and three paralogs ofCINCINNATA(CIN) in early diverging angiosperms. All class IITCPgenes have independently duplicated inAristolochiasubgenusSiphisia. AlsoCIN2genes duplicated before the diversification ofSarumaandAsarum. Sequence analysis shows that CIN1 and CIN3 share motifs with Cyclin proteins andCIN2genes have lost themiRNA319abinding site. Expression analyses of all paralogs of class IITCPgenes inAristolochiafimbriatapoint to a role ofCYCandCINgenes in maintaining differential perianth expansion during mid- and late flower developmental stages by promoting cell division in the distal and ventral portion of the limb. It is likely that class IITCPgenes also contribute to cell division in the leaf, the gynoecium and the ovules inA.fimbriata.