Chromosomal Studies On An Alpine Genus Dolomiaea (Asteraceae:Cardueae) From The Qinghai-Tibet Plateau And Adjacent Regions

The Qinghai-Tibet Plateau is an important center of biodiversity because of its high species richness and the abundance of endemic species. Chromosomal characteristics are critical in our understanding evolutionary history of species diversification. However, this formation remains unknown for a few genera, especially those in the alpine regions. In this study, we aimed to investigate chromosome numbers and karyotypes of Dolomiaea, an alpine genus occurring in the Qinghai-Tibet Plateau and adjacent regions for the first time. We reported chromosome numbers and karyotypes of10species originally descripted under Dolomiaea, one species suggested to be transferred to this genus and one species from one closely related genus Himalaiella. Two chromosome numbers, i.e.,2n=36and2n=34were found for12species. One B chromosome was observed for two species. Karyotypes of all examined species are relatively asymmetrical, classified as the Stebbins’s "3B" and "28" types. These findings suggested that polyploidizations played a minor role in species diversification of this alpine genus. However, the ancestor of this genus originated from the ancient polyploidization. The aneuploidy and karyotypic differentiation at the diploid level contributed greatly to the species diversification of this genus. In addition, paralleling decrease of the basic chromosome number also occurred in the closely related genera. Our results underscored the importance of the chromosomal data in understanding the evolutionary history of species diversification.