The evolution of self fertilisation from outcrossing ancestors is one of the principal recurring themes in plant evolution. Mimulus guttatus sensu strictu is a widespread outcrossing perennial occurring in damp environments throughout Western North America. It has colonised similar habitats in temperate regions around the world. It is the progenitor of a number of autogamous species, including M. nasutus, M. pardalis, M. laciniatus, M. marmoratus and M. cupriphilus. Two autogamous strategies are found: M. nasutus and M. laciniatus are partially cleistogamous, and anther dehiscence occurs before anthesis. In M. pardalis and M. cupriphilus anther dehiscence occurs shortly after anthesis, but floral size is much reduced so that pollen is automatically deposited on the stigma. Analysis of crosses between the various species shows that all floral characters are highly genetically correlated, and that the selfing character has evolved as a consequence of the reduction in floral size. In M. nasutus, however, a fundamental shift in allocation to male and female function has occurred. Most of the autogamous derivatives of M. guttatus have rather specialised ecologies, and autogamy may have evolved to provide reproductive assurance, but also serves to protect the co-adapted gene complex from gene flow from M. guttatus. Analysis of microsatellite variation between sympatric populations of M. guttatus and autogamous derivatives is revealing the extent to which gene flow occurs, and thus allows us to infer the adaptive value of the morphological characters distinguishing the species.

Key words: Autogamy, edaphic endemics, genetic architecture, Mimulus