An integrative approach to delimiting the Canadian Wild Ginger, Asarum canadense

Lambert, Brett

ABSTRACT: Species limits in recently diverged systems provide taxonomically challenging but essential opportunities for investigation. By incorporating various types of data, taxonomists can delimit species with more consistency, objectivity, and biological relevance. One system representing challenging taxonomy is the Canadian wild ginger (Asarum canadense) species complex. Asarum canadense is an understory, rhizomatous flowering plant species complex native to the eastern region of North America. This system displays phenotypic variation across the range, which has led to the recognition of two segregates, A. reflexum and A. acuminatum. Using genome-wide SNP data and morphological trait analysis, I applied an integrative framework to clarify species boundaries within the A. canadense complex. The resulting phylogenetic relationships show A. acuminatum diverging several times within A. canadense and the clustering among the acuminatum/canadense samples correspond to geographic proximity of samples, suggesting phylogeographic breaks may have played a role in this group’s expansion. Furthermore, A. acuminatum and A. canadense have significant morphological overlap in traits thought to be diagnostic, suggesting the acuminatum/canadense group is most appropriately treated as one species. Contrastingly, A. reflexum is exclusive or nearly exclusive in phylogenetic analyses regardless of geographic location and has little overlap among the other taxa in dimensionality reduction. In localities in which A. reflexum and the other taxa co-occurred, the samples do not group together in genetic analyses, providing strong evidence of distinctness between the species. The congruence among analyses supporting A. reflexum suggests this segregate should be recognized at the species level, which is an important finding due to the previous lack of recognition of this species by most authors.