Chromosome numbers of 24 taxa of Lamiaceae from Southwest China

Lamiaceae is the sixth largest angiosperm family and comprises over 7000 species in 236 genera distributed worldwide. China is one of the diversity centers of Lamiaceae; however, limited chromosome counts are available for Chinese Lamiaceae species. In the present study, chromosome numbers of 32 populations representing 21 species and three varieties of nine genera of Lamiaceae from Southwest China are studied, among which chromosome counts of 17 taxa are reported for the first time. Our results show that most of the species studied are diploids, and are consistent with the previously proposed base numbers. Three species, lsodon ternifolius (2n = 48), Nepeta dentata ( 2n = 32), and one population of Dracocephalum heterophyllum (2n = 24), are shown to be tetraploids. Chromosome numbers for 56 taxa of 11 genera of Lamiaceae from the Hengduan Mountains Region are obtained from published literature and present study, and the frequency of polyploidy is only 12.5%. Our study further support that polyploidy may have played a minor role in the evolutionary diversification of Lamiaceae in the Hengduan Mountains.