We examined the genetic basis for the spatial segregation of two different morphotypes within populations of Phacelia bipinnatifida, a biennial plant species associated with cove forest communities of the southern Cumberland Plateau and determined that these morphotypes were actually two distinct species. Given that there are no reported subspecies or varieties in the literature that would conform to these morphotypes, we believe we are the first to describe these morphological and genetic differences. We describe and name Phacelia sewaneensis as a new species that is differentiated from Phacelia bipinnatifida by having purple corollas, longer stamens, basal leaves without gray blotches, and more highly dissected basal leaves. Genetic analyses of individuals from sympatric populations found in three geographically distant locations on the southern Cumberland Plateau revealed that Phacelia sewaneensis (purple morphotype) was more similar genetically to purple morphotypes at the other locations than to sympatric individuals of Phacelia bipinnatifida (blue morphotype). We found that at a given site, the two species occur in large, non-overlapping, yet adjacent patches within a cove, and these patches remain homogeneous (with respect to species) from year to year. Phacelia sewaneensis prefers rocky soils and is found in higher density populations than Phacelia bipinnatifida. We establish a new epitype for Phacelia bipinnatifida and holotype and isotypes for the newly described Phacelia sewaneensis. We discuss why this new species of Phacelia has been missed by botanists, despite its multiple distinguishing features.
