Abstract
Arctic-alpine plants in the genus Saxifraga L. (Saxifragaceae Juss.) provide an excellent system for investigating the process of diversification in northern regions. Yet, sect. Trachyphyllum (Gaud.) Koch, which is comprised of about 8 to 26 species, has still not been explored by molecular systematists even though taxonomists concur that the section needs to be thoroughly re-examined. Our goals were to use chloroplast trnL-F and nuclear ITS DNA sequence data to circumscribe the section phylogenetically, test models of geographically-based population divergence, and assess the utility of morphological characters in estimating evolutionary relationships. To do so, we sequenced both genetic markers for 19 taxa within the section. The phylogenetic inferences of sect. Trachyphyllum using maximum likelihood and Bayesian analyses showed that the section is polyphyletic, with S. aspera L. and S bryoides L. falling outside the main clade. In addition, the analyses supported several taxonomic re-classifications to prior names. We used two approaches to test biogeographic hypotheses: i) a coalescent approach in Mesquite to test the fit of our reconstructed gene trees to geographically-based models of population divergence and ii) a maximum likelihood inference in Lagrange. These tests uncovered strong support for an origin of the clade in the Southern Rocky Mountains of North America followed by dispersal and divergence episodes across refugia. Finally we adopted a stochastic character mapping approach in SIMMAP to investigate the utility of morphological characters in estimating evolutionary relationships among taxa. We found that few morphological characters were phylogenetically informative and many were misleading. Our molecular analyses provide a foundation for the diversity and evolutionary relationships within sect. Trachyphyllum and hypotheses for better understanding the patterns and processes of divergence in this section, other saxifrages, and plants inhabiting the North Pacific Rim.
Highlights
Plants of the genus Saxifraga L. (Saxifragaceae Juss.) have been used extensively in the fields of systematics and phylogeography to broaden our understanding of the patterns and processes of diversification in arctic and alpine regions
Trachyphyllum (Gaud.) Koch has been largely ignored by molecular systematists even though the section resides in a basal position within the genus and likely holds valuable clues concerning the origin and evolutionary history of Saxifraga and other flowering plants of arctic-alpine regions
For the newly collected specimens, collecting permits were provided by the Arctic National Wildlife Refuge, the Gates of the Arctic National Park (GAAR2008-SCI-0001), and the Noatak National Preserve (NOAT-2008SCI-0003) and voucher specimens were archived at the Western Washington University Herbarium (WWB)
Summary
Plants of the genus Saxifraga L. (Saxifragaceae Juss.) have been used extensively in the fields of systematics and phylogeography to broaden our understanding of the patterns and processes of diversification in arctic and alpine regions. (Saxifragaceae Juss.) have been used extensively in the fields of systematics and phylogeography to broaden our understanding of the patterns and processes of diversification in arctic and alpine regions. Because Saxifraga has a primarily arctic-alpine distribution and those regions are dramatically impacted by climatic variability [1], saxifrages are excellent organisms for investigating biotic responses to climate change. Phylogenies form the basis of such studies, and have been generated for the Saxifragaceae [9], Saxifraga [10], and the major sections within Saxifraga, including sect. Trachyphyllum (Gaud.) Koch has been largely ignored by molecular systematists even though the section resides in a basal position within the genus and likely holds valuable clues concerning the origin and evolutionary history of Saxifraga and other flowering plants of arctic-alpine regions. Taxonomists agree that a thorough examination of this section is needed [14,15,16,17,18]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
