Data from: 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 monophyly, lack of introgression, and discrete rather than
continuous patterns of variation supports the recognition of all three
lineages as separate species. These results identify a surprising case of
cryptic diversity in which two broadly sympatric species have consistently
been lumped in taxonomic treatments. The clarity of our findings is
directly related to the dense sampling and high quality genetic data in
this study. We argue that there is a critical need for carefully sampled
and integrative species delimitation studies to clarify species boundaries
even in well-known plant lineages. Studies following the model that we
have developed here are likely to identify many more cryptic lineages and
will fundamentally improve our understanding of plant speciation and
patterns of species richness.