Objective Wild plant species are abundant in the Tarim River Watershed, Xinjiang of western China, many of them are rare or endemic species. However, a comprehensive survey is lacking on the taxonomy and spatial distribution of rare and endemic species in this watershed. This study aims to systematically investigate the compositional characteristics of rare and endemic plant species in this region and identify conservation priority areas to address the urgent needs of current biodiversity conservation.

Method This study focused on wild rare and endemic vascular plant species distributed in the Tarim River Watershed, and compiled records on these species from multiple data sources, including the latest list of protected species and the red list of threatened species. Life form composition, taxonomical composition, and spatial distribution of these species were analyzed based on the compiled dataset. In addition, the priority areas for plant conservation were identified based on species and phylogenetic diversity.

Result (1) The integrated plant species list consisted of 99 rare species belonging to 33 families and 60 genera, and 117 endemic species belonging to 20 families and 63 genera. Rare plants were found to be highly differentiated at both family and genus levels, and the endemic plants were highly differentiated at the genus level. Both rare and endemic plants were dominated by herbaceous species, followed by shrubs; and arbors represented life form with the smallest number of species. (2) Both rare and endemic plants were mainly distributed in the western plateau mountainous area of the watershed. Some of them were also distributed in several counties in the mid or eastern part of the watershed. (3) Six county-level priority areas for conserving plant diversity were identified, covering 85.67% of the total number of plant species in the watershed. Part of the conservation priority areas did not overlap with existing nature reserves, indicating a gap in plant diversity conservation.

Conclusion Results of this study suggest that the conservation of rare and endemic plants should be strengthened in the Tarim River Watershed. And special attention should be paid to western counties such as Wuqia, Akto, and Yecheng, as well as Hejing County in the northeastern part. In addition, this study provides fundamental data for update of relevant plant species lists and the conservation of plant species diversity.