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A floristic list of 219 species and 11 subspecies, comprising 63 families and 155 genera occurring in the Toliman grid square; an area located within the Queretaroan Semi-arid region in the southern Chihuahuan Desert, Mexico, is provided. This relatively small area is characterized by a high endemicity of flowering plant species: the floristic sample harbors 51 endemic species, and 24 species are included in some kind of risk category according to the Mexican Norm NOM-059-SEMARNAT-2010. To contribute to the protection of this flora, we performed an iterative process of complementarity analysis (beta diversity) to determine sets of priority areas for its conservation. The ranges of all species were considered by using an index that measures the average range size to determine the degree of "restrictedness" of the species. The results show that the ranges of most of the species are restricted. This flora develops within an area of high environmental heterogeneity, grouped in eight plant associations recognized by means of a numerical classification and multivariate analysis of the communities occurring in the region. Unfortunately, at present the high richness and endemism of the Queretaroan Semi-arid region are not under the legal protection of any natural reserve.