Gentiana linearis Froel. and G. rubricaulis Schwein. both occur in the Upper Great Lakes region. Although these species are closely related, they do not intergrade. They are evidently ecologically isolated, G. linearis growing in soils derived from granite and similar low-basic rocks, but G. rubricaulis in non-granitic soils. The sharpness and the extent of their differences seem comparable to those among other generally recognized species of Gentiana, and, along with features of the distribution patterns of these species, indicate that G. rubricaulis probably cannot be interpreted merely as an ecotype of G. linearis which differentiated as G. linearis spread northwestward during Wisconsin glacial recession.