Abstract
Previous analyses of chloroplast DNA restriction site data from and related genera support many relationships that are incongruent with morphological and cytological data. To find explanations for these disagreements, sequence data from the internal transcribed spacers (ITS) of nuclear rDNA were obtained from the same genera and species for comparison with chloroplast DNA evidence. Both lines of evidence supported a monophyletic Machaeranthera including and 12 additional genera, and both supported a monophyletic group of genera with chromosome numbers based on x = 6. Both lines of evidence placed stenoloba within M. sect. Sideranthus, suggesting that M. stenoloba has undergone significant morphological divergence compared to its closest relatives. Chloroplast DNA and ITS evidence disagreed substantially on the placements of M. viscida, M. heterophylla, and M. gypsitherma. Chloroplast DNA evidence suggests that M. viscida and M. gypsitherma belong within M. sect. Blepharodon and M. heterophylla belongs outside it. However, ITS evidence suggested that M. heterophylla belongs within M. sect. Blepharodon and M. viscida and M. gypsitherma belong outside it; ITS evidence suggested that M. gypsitherma is closely related to M. riparia of M. sect. Arida. The differing placements of these three species supported by chloroplast DNA and ITS evidence suggest that these species have experienced reticulate evolution. Nees, a genus of northern Mexico and the western United States, is generally charac- terized as consisting of tap-rooted annual or
Published Version
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