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Phlox phylogeny and Taxonomy
Phlox is an ecologically diverse genus of ca. 65 species occurring mostly in North America. It provides an excellent study system for plant evolutionary biology, particularly with regard to questions of adaptation, hybridization and polyploidy (whole genome duplication). Our lab has developed a comprehensive phylogenetic framework for the genus (with phylogenetic and phylogeographic work on particular clades ongoing), as well as microsatellite markers. Using these tools in concert with morphological study, we can rigorously explore species boundaries in this intriguing and taxonomically complicated group. Questions of particular interest include: What are the origins of particular taxa, what are the patterns of gene flow among populations, and what are the patterns of hybridization? What are the evolutionary and ecological implications of variation in ploidy level within taxa? What is the functional significance of differences in positional placement of reproductive parts (stigma and anthers), and have these differences been driven by selection by pollinators? How much taxonomic import should such characteristics be given, in light of species criteria relating to evolutionary history and interfertility?
Some of our current research foci are introduced below. If you are interested in learning more about work underway, please contact Carolyn Ferguson. |
We have recently completed phylogenies (based on ITS and several cpDNA regions) for the genus with comprehensive taxonomic sampling (relative to the taxonomy of the most recent monograph, that of Edgar Wherry [1955]; multiple populations of wide-ranging species are also included). As in our previous work focused on eastern North American Phlox, there is significant incongruence between these phylogenies, potentially due to processes of hybridization and polyploidy. Much recent and ongoing work in the lab focuses on development and application of low-copy nuclear regions to phylogeny development, both for the genus as a whole and for particular taxa of interest.
A “bare bones” MP phylogeny for the genus based on combined sequence data, with some general geographic and habit information. Taxa for which polyploidy is known are not included, and there is no conflict between the much reduced data sets used for this analysis.]
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One of the more interesting findings in our recent research of the genus is that Phlox not only habors many polyploid taxa, but that there is variation in ploidy level (cytotype variation, from diploid to hexaploid) within numerous taxa. Some of these taxa are widespread, variable species, while others are narrow endemics. We are using flow cytometry methods (linked to chromosome counts for taxa) to infer ploidy levels of samples, including all Phlox taxa (mirroring sampling in our genus-wide phylogenies), several polyploid complexes in the arid southwestern United States, and populations of P. pilosa in the central Great Plains. These patterns have important implications for our interpretation of phylogenies as well as a refined taxonomy of the genus.
A cartoon of flow cytometry methods used in Phlox studies (by T. Melhem)
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Population genetics of Phlox, linking to questions of species boundaries
Population genetic work on Phlox is in collaboration with Shannon Fehlberg, now at Desert Botanical Garden (Phoenix, AZ). Using microsatellites developed for Phlox in our lab, we are currently exploring 1) gene flow among species and cytotypes of several taxa in the desert southwest, and 2) population genetic patterns of a putative diploid hybrid derivative taxon (and its putative parents) within the P. pilosa species complex in the eastern U.S. In both cases, we are linking population genetic patterns to phylogenetic data for the same taxa, with an aim of applying these data to taxonomic questions.
A Phlox microsatellite region
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Floristics and refinement of taxonomy for the genus
A thoroughly revised taxonomy of the genus Phlox is an important ultimate goal of our research. The most recent monograph of the genus was the culmination of decades of valuable work by Edgar Wherry, published in 1955. Since that time, much new information has been garnered, from a diversity of genetic data to improved morphological and ecological data (including many new collections, searchable databases of collections data, and GIS-based tools for exploring geographical data). Newer data reinforce some of the previous taxon concepts, but also highlight challenges of Phlox taxonomy pointing to interesting evolutionary processes (e.g., there are cases of phylogenetic incongruence, there are complicated patterns of ploidy level variation, there is noteworthy hybridization). Recent and forthcoming Phlox floristic treatments from the lab (with collaborators) include those for the following projects: The Jepson Manual, 2nd edition (treatments for Phlox and Microsteris; in collaboration with Bob Patterson [San Francisco State University]; Steyermark’s Flora of Missouri (with assistance from George Yatskievych [Missouri Botanical Garden]; Flora of North American North of Mexico (FNA; treatments of Phlox and Microsteris; in collaboration with Bob Patterson [San Francisco State University], and Mark Mayfield [Kansas State University]). |
Phlox gladiformis, Utah
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Check back soon!
We expect the Polemoniaceae FNA work to be completed shortly, and will soon be posting a list of all Phlox taxa, along with images, recognized in that treatment. |
