In this study, 15 different types of Iranian lettuce accessions that were collected from different regions were investigated. Using root apical meristem, the number and size of the chromosomes were measured and the karyotypic formula was determined. The basic chromosome number was 9 (n=9) in all accessions and their chromosomal types were metacentric, submetacentric and subtelocentric. Analysis of variance showed significant differences between chromosomal characteristics. The maximum and minimum length of the genome was belonged to Qom (62.45 μM) and Babol (19.94 μM) accessions, respectively. Symmetrical and asymmetrical karyotypes were observed between the accessions. Formula in Ahwaz accession was 12 m + 4 sm + 2 t, which had the maximum centromic index (40.93%), while Fasa accession with 4 m + 10 sm + 4 st karyotypic formula had the minimum value (28.73). There were differences in having satellites on chromosomes between the accessions, some of them had 2 satellites, some 1 and the others had not any satellite. In principle component analysis, two components had more than 82.75% of the data variations. Based on the first and second components, the accessions separated into three groups. Cluster analysis of karyotypic traits based on UPGMA method separated accessions in three groups. The results of this study are useful for accession's classification.
