Display omitted ► Salicornia dolichostachya had its growth optimum at 300mM NaCl in the root medium. ► The highest values of succulence and stem diameter coincide with the growth optimum. ► Plants maintained a lower leaf osmotic potential than that of the medium. ► Carbon isotope discrimination decreased linear with increasing external salinity. ► Leaf and root glycine betaine concentrations did not change with external salinity. Salinization of agricultural land is an increasing problem. Because of their high tolerance to salinity, Salicornia spp. could become models to study salt tolerance; they also represent promising saline crops. The salinity-growth response curve for Salicornia dolichostachya Moss was evaluated at 12 salt concentrations in a hydroponic study in a greenhouse and at 5 different seawater dilutions in an outside setting. Salt concentrations ranged between 0mM and 500mM NaCl (≈seawater salinity). Plants were grown for six weeks and morphological and physiological adaptations in different tissues were evaluated. S. dolichostachya had its growth optimum at 300mM NaCl in the root medium, independent of the basis on which growth was expressed. The relative growth rate (RGR) in the greenhouse experiment was comparable with RGR-values in the outdoor growth experiment. Leaf succulence and stem diameter had the highest values at the growth optimum (300mM NaCl). Carbon isotope discrimination (δ13C) decreased upon salinity. S. dolichostachya maintained a lower leaf sap osmotic potential relative to the external solution over the entire salinity range, this was mainly accomplished by accumulation of Na+ and Cl−. Glycine betaine concentrations did not significantly differ between the treatments. Na+:K+-ratio and K+-selectivity in the shoots increased with increasing salinity, both showed variation between expanding and expanded shoot tissue. We conclude that S. dolichostachya was highly salt tolerant and showed salt requirement for optimal growth. Future growth experiments should be done under standardized conditions and more work at the tissue and cellular level needs to be done to identify the underlying mechanisms of salt tolerance.