Although native grasses are often desired and used for revegetation of disturbed areas, genetic differences may exist within and among natural and cultivated germplasm sources. This phylogeographic study compares geographic origin and genealogical linkages of 25 natural and cultivated germplasm sources of mountain brome (Bromus carinatus Hook. & Arn. [Poaceae]) from western North America. Significant variation among accessions (FST = 0.70) was detected by analysis of molecular variance (AMOVA), based on the number of amplified fragment length polymorphisms (AFLPs) between individual plants. Likewise, significant differences among 4 hierarchical genotypic groups, encompassing all but 5 unique accessions, were also detected (FCT = 0.47). This study identified at least one well-defined genealogical lineage, comprising 8 accessions, distributed over a broad geographic region and different ecosystems of western North America. Two other hierarchical groups, comprising 6 accessions and 3 accessions, were located within or near specific ecoregions. Results of this study indicate that natural genealogical lineages of cultivars, such as Garnet mountain brome, have dispersed and succeeded over broad geographical regions. However, more research and plant material work are needed before specific recommendations can be made over the entire species distribution.