This study presents an analysis of leaf development in 13 taxa of Papaveraceae subfamily Papaveroideae. The emphasis is on the organogenetic phase of leaf growth, during which leaflet and serrature primordia are initiated. The patterns of organogenetic activity are visualized by scanning electron microscopy and schematic drawings, and are related to regional morphogenetic and histogenetic processes, particularly thiqkening growth, surface growth, margin dilatation, and differential histogenesis. In Romneya coulteri , leaflet initiation, leaflet segmentation, and the course of higher-order segmentation proceed acropetally. In contrast, the respective patterns are basipetal in Argemone . The entire leaves of Platystemon lack segmentation. Within the closely related genera Papaver , Roemeria and Meconopsis , acropetal ( Roemeria refracta ) and divergent ( Papaver atlanticum , P. pilosum ) modes of leaflet initiation are connected by intermediate patterns ( Papaver pavoninum , P. armeniacum , P. dubium , P. somniferum and Meconopsis cambrica ). These are characterized by a divergent wave of higher-order segmentation following acropetal or simultaneous-acropetal leaflet formation. The construction of a morphocline indicates that heterochronic changes account for leaf diversification in this group. Meconopsis betonicifolia exhibits simple basipetal segmentation. Comparative observations of leaf morphogenesis in the above taxa indicate that differential marginal dilatation and histogenesis independently contribute to the determination of dissection patterns, and that leaf shape diversity arises from the potential to generate various combinations of regional growth processes.