Over half of all plant species are derived through polyploidy. However, despite the prevalence of polyploid speciation little is known about the genetic consequences of polyploidy. Three diploid species of Tragopogon were introduced from Europe to the Palouse region of eastern Washington and adjacent Idaho in the early 1900s. These species hybridized, and two allotetraploid species were formed: T. mirus and T. miscellus. The parentage of these tetraploid species is well documented, and the tetraploids are serving as models for the study of various aspects of polyploid evolution. We have reconstructed the phylogeny of Tragopogon, a largely Eurasian genus of about 50 species, using sequences of the internal transcribed spacers (ITS) of the nuclear ribosomal DNA. Our results suggest that the three diploid progenitor species of the Palouse tetraploids are distantly related. We also used DNA sequence variation in the ITS regions of T. mirus, T. miscellus, and their diploid parents to determine whether or not concerted evolution had homogenized the rDNA arrays in the tetraploids during the approximately 70-80 years since their formation. Two populations of each allotetraploid and its diploid parents were sampled, and each population was represented by three or more individuals, with four or more clones per individual. The ITS sequences of the diploid parents of T. mirus differed at 18 nucleotide positions; those of the parental species of T. miscellus differed at 16 sites. Cloned PCR products from each tetraploid match the sequence of the respective parents. These results indicate that the rDNA arrays of the recent tetraploids T. mirus and T. miscellus do not appear to have undergone concerted evolution.

Key words: Asteraceae, ITS, phylogeny, polyploidy, Tragopogon