Abstract: In this paper,chromosome numbers and karyotypes were reported for 21 populations of 13 species(including one variety) in the genus Allium L.The results showed that: basic chromosome numbers were 7,8,and 11,and polyploidy was common in the species investigated;and 2A,2B,3A types were found according to Stebbins’ karyotype classification.Three points were examined:firstly,the karyotype differentiation and evolution mechanisms of some populations in Sect.Rhizirdium G.Don;secondly,the cytogeography of A.sikkimense Baker and A.wallichii Kunth;and thirdly,the polymorphism of B-chromosomes and their significant roles in adapting to their habitats.In addition,based on our results and combined with previous cytotaxonomic studies,we suggested the karyotype evolutionary trends in Allium as:(1) The original basic chromosome number of the genus Allium is 8,and the other basic chromosome numbers evolved from the basic number 8.(2) There are two routes in the karyotype evolution of the genus Allium:one is 2A→2B→2C,which is the trend of karyotype evolution in populations with the basic chromosome number 7,while another trend in the populations with basic number 8 is 1A→2A→2B→2C.(3) Polyploidy seems to be one of the important evolutionary mechanisms for the genus Allium.