TERRITORIAL PARTITIONING OF THE CONTACT ZONE OF THE EUROPEAN MEDICAGO RIGIDULA an‎d THE CLOSELY RELATED ASIAN MEDICAGO RIGIDULOIDES IN IRAN

Medicago rigiduloides E. Small is a mostly Asian species that was recently separated from the extremely closely related, mostly European species, M. rigidula (L.) All. Medicago is a large genus of about 90 species, but there has never been a study of how any of these interact geographically where they meet. This, the first such study, documents the distribution ranges of the two species in Iran, based on 14 representative populations. The two species are extremely difficult to distinguish morphologically, so in addition to analysis of their morphology, molecular analysis of the internal transcribed spacer (ITS) region was conducted, and the degree of reliability of the diagnostic characters of the two taxa was assessed. Medicago rigidula, known to be mainly European, was found to have extended into Iran bordering the Caspian Sea. Medicago rigiduloides was found to be widely distributed in northwestern, western, southwestern, and central Iran, consistent with the hypothesis that the taxon is mainly Asian. Thus, the main distributions of the two taxa appear to be mainly parapatric, presumably related to different adaptations to the local ecology.