A numerical examination was conducted of the relationships among 99 morphological characters, geographical distribution, and ability to hybridize among the 55 species of the Old World genusMedicago(Leguminosae) currently recognized. Nearest morphological neighbours were found to be much more likely to be crossable than other species combinations. More than half of the species combinations proved to have sympatric geographical ranges. Sympatric species were not found to be significantly more crossable than nonsympatric species. Sympatry was not found to be significantly different in frequency among closely related species than among less closely related species. Using Lefkovitch's measure of biogeographical distance, a positive relationship between morphological divergence and geographical separation was demonstrated. However, the relationship was not strong. This may be due to the very large mean intercentroid distance found between the 54 pairs of nearest morphological neighbours, about 2800 km. This suggests that geographical divergence has developed so extensively between even the most closely related species ofMedicagothat random species migrations have substantially obscured relationships.