New crossing and selfing experiments withinAchillea millefoliumagg. (Compositae) succeeded with tetraploid individuals ofA. ceretanica-4 x,A. collina, A. pratensisand F1hybrids. Chromosome numbers of 105 out of 785 individuals including F1, BC, S1offsprings and free pollinated F1progenies were studied. Generally, plants were tetraploid, but occasionally aneuploids and a near-pentaploid plant originated from crossing and selfing experiments withA. ceretanica-4xandA. collina.The high degree of selfincompatibility withinAchillea millefoliumagg. is confirmed.