Hybridization between Invasive Populations of Dalmatian Toadflax (Linaria dalmatica) and Yellow Toadflax (Linaria vulgaris)

Abstract Although there is evidence that interspecific hybridization can initiate invasion by nonnative plants, there are few documented examples of novel hybridization events between introduced plant species already exhibiting invasive behavior. We conducted morphometric and molecular analyses of toadflax plants with intermediate morphology found at two sites in Montana, which were co-invaded by yellow toadflax and Dalmatian toadflax. Field-collected putative hybrid plants had intermediate morphometric scores (mean 0.47, on a scale of 0.0  =  indistinguishable from Dalmatian toadflax to 1.0  =  indistinguishable from yellow toadflax) for a suite of phenotypic traits that differentiate the parent species (leaf length ∶ width ratio, growth form, seed morphology, inflorescence type, and ventral petal shape). Inter-simple sequence repeat (ISSR) analysis of a subset of these putative hybrids revealed combinations of species-diagnostic bands, confirming the presence of DNA from both parent species. Controlled ...