RESUMEN
New data on the phylogeny of four rare and endemic species of RanunculusL.sect.Ranunculastrum DC. of western Pamir-Alai, one of which is new to science, have been obtained. Ranunculustojibaevii sp. nov., from the Baysuntau Mountains, Western Hissar Range of Uzbekistan, is described. The new species is closely related to R.botschantzevii Ovcz., R.convexiusculus Kovalevsk. and R.alpigenus Kom., but differs in the blade of the radical leaves, which is rounded-reniform, segments 3-5-dissected, each 2-5-partite with elongated, rounded apical lobes. A phylogenetic analysis, using both the nuclear ribosomal internal transcribed spacer (ITS) and cpDNA (matK, rbcL, trnL-trnF), was informative in placing R.tojibaevii in context with its most closely-related species. Discussion on the geographic distribution, updated identification key, a detailed description, insights about its habitat and illustrations are provided.