Systematics Section / ASPT
Alexander, Patrick J. , Al-Shehbaz, Ihsan , Rajanikanth, G , Bailey, C. Donovan , Windham, M. D. .
Generic affinities and fruit evolution of Athysanus and Thysanocarpus (Brassicaceae).
MEMBERS of the genera Athysanus and Thysanocarpus are winter annuals of arid and semiarid habitats in the southwestern United States. They share an unusual derived fruit morphology characterized by laterally flattened, uniovulate, indehiscent fruits. This fruit morphology suggests the possibility of a close relationship between the two genera, as do similarities in habitat, general appearance, and phenology. A family-level ITS phylogeny suggests that Thysanocarpus is a member of tribe Schizopetaleae, but the placement of Athysanus has not been previously investigated. We generated sequence data from ITS and trnL to evaluate the generic affinities of Athysanus and its possible relationship to Thysanocarpus. In addition, we used these data to investigate intrageneric relationships within Thysanocarpus. Phylogenetic analyses of these data show Athysanus to be sister to Heterodraba; these, in turn, are nested within a paraphyletic Draba (tribe Arabideae). A close relationship between Athysanus and Heterodraba is supported by both fruit and trichome morphology. This clade is far removed from Thysanocarpus in both analyses, indicating that the derived fruit morphology shared by Athysanus and Thysanocarpus results from convergent evolution. Of the five species currently recognized in Thysanocarpus, four were included in our analysis. These four species show markedly different relationships in the two molecular data sets, reflected in both branching order and taxon monophyly. The trnL analysis weakly supports T. radians as sister to all other species of Thysanocarpus and places T. laciniatus within a paraphyletic T. curvipes. The ITS analysis strongly supports T. conchuliferus and T. laciniatus as sister to the rest of the genus and identifies T. curvipes as monophyletic.[c.e.:srb]
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1 - New Mexico State University, Department of Biology, Po Box 30001, Department 3Af, Las Cruces, New Mexico, 88003-8001, USA
2 - Missouri Botanical Garden, Po Box 299, St Louis, Missouri, 63166-0299, USA
3 - University of Utah, Utah Museum of Natural History, 1390 E Presidents Circle, Salt Lake City, Utah, 84112, USA
Presentation Type: Oral Paper:Papers for Sections
Location: 134/Performing Arts Center
Date: Tuesday, August 1st, 2006
Time: 11:30 AM