Biogeography, ecology, and evolution of the endemic vascular flora of the glaciated Great Lakes region: A case study of the Solidago simplex species complex

Pleistocene glacial activity transformed the Great Lakes basin into a natural laboratory where the effects of past glaciation on the development of the regional flora and the evolution of endemic species can be readily examined. This dissertation focuses specifically on the ecology and evolution of the endemic flora of the Great Lakes region. Chapter II characterizes biogeographic and ecological patterns of the 60 endemic vascular plants that have been described from the region. The majority of these plants are restricted to specialized habitats in the northern Great Lakes region. Many of these endemics have been hypothesized to be recently evolved edaphic specialists, but the evolution of the vast majority remains unstudied. Chapters III, IV, and V examine cytogeographic, phylogeographic, and ecological patterns in Solidago simplex across North America and in the Great Lakes region. Cytogeographic studies revealed patterns that were more complex than previously realized. This data combined with phylogeographic analyses of cpDNA suggest that (1) tetraploids within Solidago simplex formed multiple times, (2) the Great Lakes region was populated by migrants from multiple glacial refugia, (3) the southeastern United States and Beringia were not primary sources of postglacial migrants into the Great Lakes region, and (4) there is a significant biogeographic connection between the Great Lakes region and the Rocky Mountains. Field and herbarium studies revealed that Solidago simplex populations in the Great Lakes region are separated by a combination of cytological, ecogeographic, morphological, and phenological differences. These data suggest that the Great Lakes region harbors at least three reproductively isolated species. Diploid plants in the northern Great Lakes region are referable to Solidago simplex var. simplex. The sand dune endemic, S. simplex var. gillmanii, is ecologically and morphologically distinct from all other entities in the region and should be elevated to species status. Tetraploid rock outcrop plants, normally recognized as S. simplex var. ontarioensis, represent at least two distinct entities. Their evolution and circumscription require additional study. Overall, this research indicates that a complex Pleistocene history and adaptation to specialized habitats has driven diversification and speciation in Solidago simplex and likely the broader endemic flora as well.