Karyological investigations on several species of genus Rebutia Sect. Digitorebutia (Cactaceae).

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 identified. 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 first time. In this species, four populations with hexaploidy (2n=6x=54) were detected for the first time. Results indicate that poly- ploidy is confirmed as the most significant 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.