Aim and background.Sainfoin (Onobrychis) in Iran with 63 annual and perennial species that are distributed in different climatic regions of distribution. Some species of this genus are used for value of forage and erosion control and plants to attract visitors as honeybees. These species have high genetic diversity and can be used as valuable genetic resources in breeding of cultivated species.

Materials and Methods. Nine species of of sainfoin were collected from natural habitats across Iran. Number and size of chromosomes as well as karyotypic formula of the populations were measured and studied using their root tip meristemes.

Results.The basic chromosome number varied between x=7 and x=8 and their chromosomal type was metacentric and sub-metacentric. According to average genoms length, the highest was for O. scrobiculata (24.26) and the lowest belongs to O. lunata (14.76). According to Stebbins' classification, O. heliocarpa and O. lunata are classified as symmetric class of A and others as B. O. heliocarpa with 16m formula had the most total form percentage (44.856) and lowest intra chromosal asymmetrical and O. oxyptera with 2m+ 14sm had lowest TF% (32.552) and the most asymmetrical karyotype. Dendrogram results from cluster analysis (Ward) based on the karyptipic parameters species were classified in to two classes. The highest distance was obtained between O. oxyptera and O. heliocarpa and the lowest metric distance value was obtained between O. buhseana and O. atropatana.

Conclusion. The results of this analysis for species classification and selection of species were close to each other as to perform crosses between species