An overview on cytogenetics of the genus Onobrychis (Fabaceae) with special reference to O. sect. Hymenobrychis from Iran

The present study reports the chromosome number and meiotic behavior of 25 populations belonging to 10 species of Onobrychis sect. Hymenobrychis from Iran. Most populations showed the chromosome number 2n = 2x = 14. However, the chromosome number of two populations belonging to O. michauxii and O. subnitens was 2n = 2x = 16. It seems that the species with x = 7 are derived through aneuploid loss. In addition, intra- and interspecific variations in the chromosome number within O. sect. Hymenobrychis, aneuploidy and polyploidy in Onobrychis with special reference to the section Hymenobrychis and also the evolution of the chromosome number throughout the genus are discussed here. As the result of the present study and by reviewing the chromosome number within the genus, it can be concluded that O. sect. Hymenobrychis includes comparatively highly derived taxa and can be considered as a heterogeneous unit within the genus Onobrychis. Almost all the studied taxa displayed regular bivalent pairing and chromosome segregation at meiosis. However, some meiotic abnormalities observed in different taxa are discussed here.