Abstract Aim Self‐pollinating plants (‘selfers’) have larger geographical ranges and inhabit higher latitudes than their outcrossing relatives. This finding has led to the hypothesis that selfers also have broader climatic niches (‘niches’) because the increased likelihood of successful colonization into new areas and the initial purging of deleterious mutations could offset the inability of selfers to adapt to new environments owing to low heterozygosity. Here, we examine the niches of hundreds of closely related selfing and outcrossing species to determine whether selfers do indeed have larger niche breadths. Location Global. Time period Current. Major taxa studied Twenty clades of flowering plants comprising 424 species. Methods We estimated and compared the climatic niches of 194 pairs of sister species across 15 families, which differed in mating system. We incorporated these results into models predicting niche breadth and its change over time to estimate the effects of mating system on niche breadth. Furthermore, we compared the degree of niche divergence between sister‐species pairs of various mating system combinations. Results Selfers did not have wider niche breadths than their outcrossing sister taxa. Sister pairs of selfers also exhibited greater niche overlap than outcrossing sisters, implying that niche expansion becomes limited after the transition to selfing. Furthermore, the niche breadth of selfers was predicted to decrease significantly faster than that of closely related outcrossers. Main conclusions Our results demonstrate a decoupling in the range size and niche breadth of selfers. The larger geographical range and comparable niche breadths of many selfers is most likely to be a temporary phenomenon caused by a transiently expanded realized niche, and both will become constricted over time in comparison to outcrossers.