Increased salinity affects plants by toxic ion effects and by lowering soil water potential, which makes it difficult for plants to take up water. Salt marshes in Kansas are characterized by highly saline soils, but interspecific variation of photosynthesis and water potential in inland salt marsh species has been largely unexplored. Comparisons between species can help give a better understanding of how saline environments are tolerated by different plants. It was hypothesized that non-native Tamarix ramosissima has a greater tolerance to high salinity by maintaining lower water potential compared to the native species Spartina pectinata and Distichlis spicata. In this study, all three species were grown under controlled salinity treatments in a greenhouse experiment to determine if photosynthesis or water potential differ between species. Individuals of T. ramosissima, S. pectinata, and D. spicata were grown in 0, 15, or 30 g L^-1 salinity under greenhouse conditions for two weeks. Photosynthesis was reduced in all species under high salinity and stomates were particularly sensitive to increasing salinity in T. ramosissima. Individuals of non-native T. ramosissima were able to lower water potential to a greater extent than native D. spicata and S. pectinata. There is physiological tolerance to high salinity in all species, helping them to survive in conditions of Kansas salt marshes.