Background: More than 60 species of the genus Lathyrus are distributed in Southwest Asia. It is the second largest genus of the tribe Fabeae, after Vicia, in the region (and in Iran with 23 species). In the regional Flora (Flora of Turkey, FloraIranicaand flora of Iran), the genus has been divided into 9-10 sections. Here we analyzed the phylogeny of Lathyrus and its relationship with Pisum based on plastid gene matK sequences. Objectives:The present study utilized several approaches including maximum parsimony, Bayesian and maximum likelihood methods to evaluate the monophyly and relationship within the genus Lathyrus, both at the sectional level and species level, mainly based on the taxa growing in Iran. Materials and Methods:A total of 52 accessions, representing 38 species of Lathyrus, three species of Pisum and four species of Vicia and Lens as out-groups, were analyzed for reconstructing the phylogenetic relationship using chloroplast gene matK sequences. Maximum parsimony, Bayesian and maximum likelihood methods were used to construct phylogenetic trees. Results:The present study indicated that Pisum was nested among Lathyrus species. Two members of the Lathyrus section, Clymenum (Lathyrus ochrus and L. Clymenum) with Pisum, formed a weakly supported clade as sister to the larger polytomy comprising the remainder of the Lathyrus species. Several sections of the Lathyrus including Lathyrostylis, Lathyrus and Clymenum were monophyletic. Lathyrus roseus (of the monotypic section Orobon) were nested among the members of section Lathyrus. The newly taxon described species L. alamutensis, endemic to Iran, were nested among other species of Lathyrostylis. Linearicarpus, Orobus and Pratensis were not monophyletic sections. Pratensis and the monotypic section Aphaca were the closest taxa. In our analysis, L. Pratensis formed a sister group relationship with the Aphaca clade, not its own section. Conclusions:Shimodaira-Hasegawa (SH) test of the matK dataset showed that all analyzed Lathyrus species formed their own clade and Pisum was sister to them. Furthermore, when we removed the two above-mentioned Lathyrus species, the analysis retrieved Pisum, as a well-supported clade being sister to the Lathyrus calde.