The Slovak part of the Western Carpathians provides a suitable ecological conditions for the occurrence of two closely related species of the Tanacetum corymbosum group. Previous karyological research has revealed two different cytotypes (Tanacetum clusii 2n = 2x = 18 and Tananacetu corymbosum 2n = 4x = 36), and the observations of florists show their morphological differences. As the data from these studies were based on only a small set of populations, the aim of the present thesis is to provide a more comprehensive overview of the karyological and morphological variability of Tanacetum corymbosum group in the study area. We confirmed the existence of two known cytotypes corresponding to the taxa T. clusii (2n 2x 18) and T. corymbosum (2n 4x 36) on a sample of 530 individuals (45 populations) by flow cytometry. This revealed other cytotypes in 7 individuals. Probable triploid (2n 3x 27) and pentaploid (2n 5x 45), as well as individual with a presumable aneuploid cytotype (2n 4x 36–2). Univariate and multivariate analyses by examining 10 morphological traits on a set of 351 individuals (39 populations) and on 2 traits of the achenes (180 achenes from 6 populations) confirmed the tendency of individuals to aggregating into two groups corresponded to the diploid and tetraploid cytotypes. Morphometric analyses have shown the most strongly influencing trait of this differentiation is the color of the margin on the involucral bracts, which is markedly dark brown to black in T. clusii, while in T. corymbosum it varies in lighter shades of brown to yellow brown. However, by combining the examined quantitative traits, it is possible to diagnose an individual correctly to more than 91%. From the results of the relative amount of DNA of the monoploid genome of the studied individuals, in combination with the results of multivariate morphometric analyses we conclude the autoploid origin of individuals with triploid and pentaploid cytotypes collected in single-cytotype populations. The exception is one triploid individual, originating from the contact zone of the diploid and tetraploid population, in which case we assume a presumable hybrid origin.