A New Chromosome Number Report in Stachys L. Species by Use of Karyological Analysis

Abstract

The somatic chromosome numbers and karyotype features of seven populations representing three species of Stachys L. (Lamiaceae), which are naturally distributed across Iran, were described. The results confirm the presence of different basic chromosome numbers including x = 15 and 17 within the genus. All the studied taxa were diploid and the chromosome counts of two species including S. benthamiana and S. setifera (2n = 34) are reported for the first time, while the chromosome number of S. byzantina (2n = 30) is confirmed. The chromosomes in the studied taxa of Stachys were generally small, as the longest chromosome length was detected on S. setifera (18713) (2.26 μm), whereas S. setifera (23354) demonstrated the shortest length (1.46 μm). The karyotypes were symmetrical composing of metacentric chromosomes as indicated by their mean arm ratio (AR) that ranged between 1.11 in S. setifera (23354) and 1.29 in S. byzantina (37985), so it was classified as class 1A according to Stebbins’ categories. Based on the values of total form percentage (TF%, 47.1%), Arano index of karyotype asymmetry (AsK%, 52.5%), symmetry index (S%, 94.0%) and differences of range relative length (DRL, 0.36), S. setifera (23354) had the most inter-and intra-chromosomal symmetric karyotype. Also, S. byzantina (37985) had the most inter-and intra-chromosomal asymmetric karyotype based on the values of TF% (42.0%), AsK% (56.1%), and relative length of chromosome (RL%, 6.6%). The results of cluster analysis based on chromosomal parameters divided the taxa into two main groups using the Ward method. Group I included taxa with x = 17 and group II contained S. byzantina (x = 15).

Keywords

• asymmetry index
• chromosome numbers
• karyotype
• stachys