Cytological Study on Acorus L. in Southwestern China,with Some Cytogeographical Notes on A. calamus

Chromosome counts of three Acorus species ( A. calamus L., A. tatarinowii Schott and A.　gramineus Soland.) were performed in the Southwestern China. Both A. tatarinowii and A. gramineus shared the same chromosome numbers 2n=24. Populations of A.calamus in South and Southwestern Yunnan are tetraploids (2n=44) while those in the central and northwestern Yunnan being hexaploids (2n=66). The hexaploids are reported here for the first time. Attention was drawn to the ploidy pattern in A.calamus . It seems that the hexaploids were evolved from their ancestors during the early Tertiary as an impact of orogenesis of the Himalayas.