The classification of butterflies in the widely recognized genus Morpho previously used subgenera that were assumed to constitute natural species groups. Cladistic analysis of 120 characters provided a well-resolved tree showing that some subgenera do not constitute monophyletic groups. This study supported some traditional taxonomic species groupings, but rejected the concept of subgenera for Morpho. Therefore, we formally redefined the genus to be consonant with the assumptions of phylogenetic classification. Predictions about Morpho life histories, the correlation of color pattern and flight behavior with vertical flight height, and the evolution of sexual dimorphism are discussed in light of our phylogeny.