Compare Gomphonema marriae

In the past, this taxon may have been included in the Gomphonema gracile species complex. Some taxa have been recognized as distinct within the complex, but it likely contains many distinct species that have not been formally described and practitioners are advised to assign names tentatively for the time being. In general, the G. gracile lectotype (Reichardt 2015) has a broader headpole and bluntly rounded ends, with a shape that is not rhombic-lanceolate nor naviculoid.

Gomphonema graciledictum has a higher stria density, narrower valves, more rounded apices, and proximal raphe ends that deflect toward the stigmoid. Areolae are C-shaped (SEM feature).

 Gomphonema naviculoides has a higher areola density and proximal raphe ends deflect toward the stigmoid. Areolae are C-shaped (SEM feature).