Premise of the study: Arbuscular mycorrhizal (AM) fungi can promote plant growth and reproduction, but other plant physiological traits or traits that provide defense against herbivores can also be affected by AM fungi. However, whether responses of different traits to AM fungi are correlated, and whether these relationships vary among plants from different populations is unresolved. Methods: We assessed whether different populations of the perennial forb, Asclepias speciosa, grown from seed collected from different environmental conditions across its distributional range respond differently to AM fungi, and if the responses of six growth and defense traits are correlated. Key Results: Although there was strong genetic differentiation in mean trait values among populations, AM fungi consistently increased expression of most growth and defense traits across all populations. Responses of biomass and root:shoot ratio to AM fungi were positively correlated, suggesting that plants that are more responsive to AM fungi allocated more biomass belowground. Responses of biomass and trichome density to AM fungi were negatively correlated, indicating a trade-off in responsiveness between a growth and defensive trait. Conclusions: Our results suggest that while there is substantial population differentiation in many traits of A. speciosa, populations respond similarly to AM fungi, and both positive and negative correlations among trait responses occur.