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The majority of species used for revegetation in semi-arid western rangelands of North America are grasses, with few forbs and nearly no legumes. Astragalus filipes (Ton. Ex A. Gray) is a western North American legume and a promising candidate for use in rangeland revegetation, but assessments of plant species diversity and structure are necessary to determine which collections should be used to constitute a conservation unit or regional seed source. To address this issue, we characterized within-collection genetic diversity, identified genetically differentiated groups, and tested genetic correlations with environmental variables on 67 collections of A. filipes. Within-population genetic diversity was greatest for collections in Oregon and lowest for collections in British Columbia and central Nevada. Five genetically differentiated groups were detected: one with strong support from central Nevada, one with strong support from British Columbia. and three with weak support comprising all other collections throughout Oregon. Washington, California. Idaho. and Nevada. Although there was significant correlation between genetic and linear geographic distance matrices, there was no correlation between genetic and phenotypic, elevation, temperature, or precipitation distance matrices. These results show that geographic distance contributes to genetic differentiation, and that structured populations have occurred in northernmost and southernmost groups of collections of A. filipes.