XVI International Botanical Congess

Corallorhiza is a genus of non-photosynthetic orchids that obtain carbon via parasitism of ectomycorrhizal fungi. We are using this interaction as a model to study the evolution of symbiotic specialization and speciation in plants. Molecular phylogenetic analyses reveal that each Corallorhiza species is narrowly specialized. Specificity toward fungal families has evolved conservatively within Corallorhiza (few major host switches), but specificity toward fungal species is evolving rapidly (ubiquitous minor host-switches). These orchids have recently radiated onto older fungal clades rather than co-speciating with them. At least one Corallorhiza species appears to be undergoing cryptic speciation and host-race formation. We are currently testing whether specialization is driving speciation in Corallorhiza.