According to this interpretation, the obligate halophytes are plants which for their normal development need certain ions of the alkali metals and halogens, and which, therefore, can exist and bear seed only in soils containing salt. They also can live in soils where the respective salts have accumulated in such quantities as to be fatal to most  other plants. Halophytic vegetation taken as a whole should permit of classification into various types according to the presence or absence in the soil solution of certain of the ions of sodium chloride, or of sulphates of potassium, calcium, or magnesium. The specific ionic effect should be reflected by the floristic composition of the vegetation, even though, as Gola (1910) states, a partial substitution of NaCl by MgCl2 or CaCl2 may be possible. (Braun-Blanquet 1932:194-5)
BRAUN-BLANQUET, Josias. 1932. Plant sociology: the study of plant communities. (Trans.: George D. Fuller; Henry S. Conard) New York: McGraw-Hill Book Company.