Polyphyly of the genus Dentaria (Brassicaceae):: Evidence from trnL intron and ndhF sequence data

Members of the traditional genus Dentaria (Brassicaceae) comprise about twenty species disjunctly distributed in three biogeographical areas: eastern North America, western North America, and Eurasia. The group has variously been treated as a distinct genus, as a subgenus of Cardamine, or as several sections within Cardamine. Using chloroplast DNA sequence data from the trnL intron and ndhF gene we examine the evolutionary relationships of traditional Dentaria species to Cardamine sensu stricto and the validity of Schulz's sectional treatment of Cardamine (including Dentaria). Sequence data were obtained from nine Dentaria species, representing all three disjunct biogeographical groups and two of Schulz's sections, and six other Cardamine species representing a range of morphological variation within the genus and three of Schulz's sections. Results from maximum parsimony analysis show multiple origins for Dentaria within Cardamine and do not correspond well to Schulz's sectional classification. Cardamine including Dentaria appears to form a monophyletic group with Nasturtium as its sister-group. We also find strong support for monophyly of the eastern North American species group previously placed in the genus Dentaria. Further, we find that C. clematitis and C. flagellifera, considered by some to be conspecific, are distinct and not closely related.