Gomphonema mexicanum has a higher stria density, more narrow apices and a lower L:W ratio. Gomphonema ventricosum has a broader axial area, especially at the central area, and higher stria striae at mid-valve. Gomphonema manubium is more robust, with a much broader axial area and higher areola density than G. mehleri. Gomphonema submehleri has a higher stria density and narrower valves than G. mehleri. Gomphonema gibba has a narrower headpole and less coarse stria. Note also, that similar but undescribed species, are present in the southeastern states.