LAUSR

Abstract Polygonum s.str. (Polygonaceae) is a genus with three basic chromosome numbers (x = 10, 20, 30) and different ploidy levels (from diploid to octaploid). In this study, karyological characteristics and mitotic numbers were presented for six annual species and subspecies of Polygonum sect. Polygonum in Iran (P. aviculare subsp. buxiforme, P. aviculare subsp. depressum, P. arenastrum, P. patulum, P. argyrocoleon and P. olivascens). Ploidy levels varied from diploid to pentaploid. There is not any correlation between genetic diversity previously studied and ploidy levels in taxa. Three counts are new while three records confirmed previous studies. All species have metacentric chromosomes. The studied taxa differed in the size of their chromosomes and in karyotype formula indicating the role of quantitative change in the chromatin (DNA) material as well as chromosomes structural changes in the species diversification.