Exceptional diversification of floral form in a specialized pollination mutualism

Floral morphology plays a key role in facilitating the mechanical fit between pollinators and plant reproductive organs, allowing for successful reproduction. In this study, we test how independent origins of pollination by scent-collecting male euglossine bees ('perfume flowers') have influenced the evolutionary dynamics of floral shape across the diverse neotropical Cymbidieae orchid radiation. We characterized morphological variation across 178 species (c. 5% of total diversity) spanning 86 genera (c. 54%) and 8 subtribes (100%) to provide the first quantitative description of morphospace within this clade. We fit a model of multivariate character evolution to a phylogenetically diverse subset of this dataset consisting of 67 orchid species across 65 genera to rigorously characterize the role of pollination mode on rates of flower shape evolution. Perfume flowers exhibit up to 7.8-fold higher rates of phenotypic evolution compared with plants utilizing other rewarding or deceptive mechanisms. Our results provide novel insights into the capacity for pollinators to influence the pace of floral evolution across a diverse radiation, providing an engine for trait diversification in some of the world's most floristically rich regions.