Phylogeny of Onobrychis sect. Hymenobrychis (Fabaceae) based on chloroplast DNA sequence data

Phenetic analysis of morphological characters in different species of Onobrychis Miller sect. Hymenobrychis DC. (Fabaceae), classified them in two main groups based on corolla features. To determine the phylogenetic relationships among the 13 species, chloroplast DNA sequences were used. Analysis of these data resulted in a well-resolved and well-supported phylogeny. Phylogenies generated by maximum likelihood show monophyly of O. sect. Hymenobrychis and the division of the section into two major clades. The first branching clade was formed by all the species of the section with large flowers, a yellowish corolla with or without venation and some species having a larger chromosome number (x=8 vs x=7). The second major clade includes the remaining species studied, all of which have small flowers, a yellowish corolla with or without venation or purple maculae and the common number of chromosomes (x=7). The compliance of the molecular, morphological and cytogenetic data indicates that x=8 is ancestral in the section and x=7 are derived through an aneuploid loss of a chromosome. The resulting phylogeny suggests the Zagros area as an origin of evolution in the sect. Hymenobrychis, followed by a radiation to the Alborz area in Iran.