Most studies of multivariate evolution on the floral phenotype assume that traits evolve independently one from each other, ignoring the modular structure that results from genetic correlations or developmental constraints. In this paper we describe the interdependence of nine floral traits in the herb Mimulus luteus var. luteus (Phrymaceae), as an attempt to characterize functional modules on which natural selection can potentially act upon. Using edge exclusion deviance analysis, we detected four modules: (a) an attractiveness module, (b) a stigma behavior module, (c) a stigma surface module, and (d) a herkogamy module. Consequences of these findings for future studies of natural selection in this species are discussed