Schenk, John J. , Hufford, Larry .
A Phylogenetic Analysis of Mentzelia Section Bartonia (Loasaceae).
Mentzelia section Bartonia (Loasaceae), a monophyletic group that is widely distributed in arid regions of the American West, has presented considerable taxonomic difficulties. We have used a phylogenetic approach to infer major clades, address circumscription concerns, and to explore for undescribed diversity in section Bartonia. We applied nucleotide sequence data from the internal and external transcribed spacer regions of nrDNA for phylogeny reconstructions using maximum likelihood analyses. Reconstructions indicate that section Bartonia consists of two well-supported clades, each consisting of numerous species. One clade consists of the Great Plains M. decapetala and its sister, which is restricted to taxa from the intermountain region and includes species that Holmgren and Holmgren denoted as subshrubby. The other major clade was more widespread and included, notably, taxa from the Chihuahuan and Sonoran deserts as well as the Great Plains, Rocky Mountains, and intermountain region. Our phylogenetic results and Bayesian and Shimodaira-Hasegawa hypothesis tests indicate certain species, for example M. pumila and M. multicaulis, when treated broadly, represent polyphyletic assemblages. We find that modern treatments of M. multiflora are highly polyphyletic, and we suggest a narrow circumscription of this taxon to include only populations in the Southern Rocky Mountains. Such a delimitation of M. multiflora points to several other lineages in section Bartonia, generally treated as part of this species, that are independent evolutionary lineages. For example, Mentzelia multiflora subsp. longiloba is an evolutionary lineage independent from M. multiflora, and we recognize M. longiloba as a variable complex, possibly encompassing cryptic species, which is centered along the US-Mexico border from California to Texas. Our phylogenetic studies have also pointed to the discovery of undescribed diversity, including a new species from the Grand Canyon that has both a subshrubby growth habit and narrow distribution that are typical of taxa on the Colorado Plateau.
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1 - Washington State University, School of Biological Sciences, 312 Abelson Hall, PO Box 644236, Pullman, WA, 99164-4236, United States
2 - Washington State University, School of Biological Sciences, Po Box 644236, Pullman, Washington, 99164-4236, USA
Presentation Type: Oral Paper:Papers for BSA Sections
Location: Cottonwood D/Snowbird Center
Date: Monday, July 27th, 2009
Time: 8:15 AM