Arbuscular mycorrhizal fungi (AMF) colonize roots and provide phosphorus as well as other benefits to hosts in exchange for photosynthate. I explored how the symbiosis between AMF and the native prairie forb Gaillardia aristata differed regionally among sites that varied in soil phosphorus availability (SPA). In the field, plant biomass and shoot phosphorus concentration were correlated with SPA and hyphal length. AMF community composition in roots correlated with distance between sites, SPA, temperature, and precipitation. To test the hypothesis that AMF from sites varying in SPA would differ in effectiveness at provisioning phosphorus to their host, I grew G. aristata in the greenhouse with soil inoculum from sites low and high in SPA and fertilized with or without phosphorus. Gaillardia aristata benefited equally from both inocula and phosphorus fertilization, while root AMF communities differed between inocula but not with fertilization. AMF from varying SPA appear to be equally effective mutualists.