-Mitotic chromosome numbers are reported for fourteen populations of Tanactum polycephalum Schultz Bip. (L.) collected from west of Iran. In T. polycephalum, chromosome numbers were varied from 2n= 2x=18 to 2n=6x= 54. One diploid population (2n=2x=18) and two populations with both diploid and tetraploid chromosome numbers (2n=2x=18 and 36) were identifi ed. Five populations with chromosome number (2n=4x=36) and a population with two different chromosome numbers (2n=4x=36 and 54) were found for the fi rst time. In this species, four populations with hexaploidy (2n=6x=54) were detected for the fi rst time. Results indicate that polyploidy is confi rmed as the most signifi cant evolutionary trend in chromosome number within this species. This species is also a problemic and polymorph taxnon and our results indicate that its polyploidy can be regarded as the reason.