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Phylogenetic analyses have suggested that Mathewsia is not monophyletic because of the exclusion of M. nivea from a well-supported clade comprising the remaining species of the genus. This result suggests that M. nivea should be recognized as a new taxon in Brassicaceae. Nevertheless, the lack of phylogenetic placement and limitations in morphological differentiation from other Mathewsia species preclude its practical recognition. Phylogenetic and hypothesis testing analyses were conducted to elucidate the possible tribal position of M. nivea in Brassicaceae. At the same time, ecological niche for M. nivea and Mathewsia species was modeled to evaluate a possible climatic and geographic circumscription for both taxa. Phylogenetic analyses supported a most likely tribal affinity, but not the inclusion, of M. nivea with Schizopetaleae, supporting previous molecular and morphological evidence. Ecological niche model analysis revealed non-overlapped areas of occurrence between M. nivea with M. auriculata and the remainder of the genus Mathewsia, implying that M. nivea occurrs in a different ecological niche than Mathewsia in the Andes. Therefore, the new monotypic genus Atacama and its species A. nivea are defined. This circumscription reveals important insights about the diversification of Schizopetaleae, as close relationship of A. nivea with Schizopetaleae could help the comparative analysis of biological adaptations to aridity. Likewise, the concomitant discovery of A. nivea with other monotypic taxa of Brassicaceae in the area might suggest possible areas of co-diversification in Andean-arid latitudes of South America.