A synopsis of the genus Rheum (Polygonaceae) in Iran with description of three new species

According to previous studies, the genus rheum in iran includes four species: r. turkestanicum janisch.,r. persicum losinsk., r. ribes l. and r. khorasanicum baradaran & jafari. during the long-term study, based on field and many herbaria specimens, three new species including r. iranshahrii taheri & assadi sp. nov., r. kordestanicum taheri & assadi sp. nov. and r. austro-iranicum taheri & assadi sp. nov. were discovered in iran. in this paper, all new species are compared with their putative relatives. botanical characters are elaborated and a brief taxonomic synopsis for all accepted species is also provided.