Artesian springs of arid inland Australia provide permanent water that supports naturally fragmented wetland communities. Some plant species that occur at springs have more extensive populations in coastal wetland areas of Australia where they may experience quite different environmental conditions. The present study investigated the growth response of one such species, Baumea juncea (R.Br.) Palla (Cyperaceae), to salinity and waterlogging. Plants from each region were subjected to combinations of salinity (freshwater or 20% seawater) and waterlogging (unsaturated or saturated soil), in a factorial design, for a period of 5 months. All plants survived and although the final aboveground biomasses did not differ significantly among the treatment combinations, for spring plants, the relative growth of roots was greater in unsaturated soil than in saturated soil. For the growth parameters of total biomass, culm biomass and rhizome biomass, spring and coastal plants showed contrasting responses to the treatment combinations; for spring plants in fresh water, these parameters were greater in the saturated treatment than in the unsaturated treatment, whereas for spring plants in saline water, these variables were lower in the saturated treatment than in the unsaturated treatment. Coastal plants displayed the reverse pattern. For the remaining parameters of root biomass, root:culm ratio and aboveground:belowground biomass ratio, plants from spring and coastal regions grown under saline conditions displayed contrasting responses to waterlogging. Our findings showed that the growth responses of plants of B. juncea to waterlogging and salinity differ for spring and coastal plants, suggesting potential differential adaptation by populations in these disjunct and distinct environments.