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Chromosomal studies on the alpine genus Dolomiaea (Asteraceae: Cardueae) from the Qinghai-Tibet Plateau and adjacent regions

Chromosomal characteristics are important for our understanding of the evolutionary history of species diversification. However, these characteristics are as yet unknown for some plant genera, especially those in alpine regions. In this study, our aim was to investigate the chromosome numbers and karyotypes of Dolomiaea, an alpine genus occurring in the Qinghai-Tibet Plateau and adjacent regions, for the first time. We report the chromosome numbers and karyotypes of 10 species originally assigned to Dolomiaea, one species which has been suggested should be transferred to this genus and one species from the closely related genus Himalaiella. Two chromosome numbers, i.e. 2n = 36 and 2n = 34, were found in these 12 species. One B chromosome was observed in two species. Karyotypes of all the species examined are relatively asymmetrical, and are classified as Stebbins’ types 3B and 2B. These findings suggest that polyploidization events played a minor role in species diversification in this alpine genus. Aneuploidy and karyotypic differentiation at the diploid level, instead, contributed greatly to species diversification in this genus. However, many lines of evidence indicate that the ancestor of the genus originated from an ancient polyploidization event. In addition, our results provide cytological evidences of the transference of Frolovia frolovii and Saussurea costus to Dolomiaea, a recent proposal based on molecular phylogenetic context.