Twelve accessions of thyme medicinal plant belonging to Iranian species of thymus pubescens, T. carmanicus , T. fallax, T. kotschyanus and T. daenensis were studied in aspect of cytogenetical marker. Root tips were examined for karyological studies. Two ploidy levels (diploid and tetraploid) and two chromosome numbers (30, 60) were recognized.Type of chromosomes in all of populations were metacentric (m), and located in 1A except for T. kotschyanus-2(Qom-Karamjegan) with 6sm+24m karyotype formula and 2B stebbins classes. The size of mitotic chromosomes was very small and the mean length of total chromosome varied 0.849 mm in T daenensis-3(Isfahan) to 1.626 mm in T. kotschyanus-2(Qom-Karamjegan). In addition, T. kotschyanus-2 with the highest of A1 and A2 (interachromosomal and interchromosal asymmetry index) had karyotype heterogeneity. The results of principal components analysis (PCA) and cluster analysis (Ward) separated all of populations based on ploidy levels and karyotypic traits.
