Restriction-site-associated DNA sequencing reveals a cryptic viburnum species on the North American coastal plain

Species are the starting point for most studies of ecology and evolution, but the proper circumscription of species can be extremely difficult in morphologically variable lineages, and there are still few convincing examples of molecularly-informed species delimitation in plants. We focus here on the Viburnum nudum complex, a highly variable clade that is widely distributed in eastern North America. Taxonomic treatments have mostly divided this complex into northern (V. nudum var. cassinoides) and southern (V. nudum var. nudum) entities, but additional names have been proposed. We used multiple lines of evidence, including RADseq, morphological, and geographic data, to test how many independently evolving lineages exist within the V. nudum complex. Genetic clustering and phylogenetic methods revealed three distinct groups—one lineage that is highly divergent, and two others that are recently diverged and morphologically similar. A combination of evidence that includes reciprocal monophy...