Gomphonema americobtusatum

Valves are lanceolate and slightly heteropolar. Valve apices are obtuse and weakly protracted in some specimens, not protracted in others. The axial area is narrow and linear in smaller specimens, moderately wide and lanceolate in larger specimens. The central area is slightly asymmetric and transversely rectangular. It is bordered by one or two shortened striae on the primary side adjacent to the stigma, and one or two shorter striae on the secondary side of the valve. The raphe is lateral and somewhat sinuous. External proximal raphe ends are weakly expanded and slightly deflected toward the primary side. Terminal raphe ends are are sinuous and deflected toward the secondary side of the valve. Striae are parallel or slightly radiate at the valve center, and become more radiate toward the apices. Areolae in the striae number 28-34 in 10 µm. An initial valve was observed at 55 µm in length.

The relation between this taxon and G. angustatum var. obtusatum (Kützing) Grunow in Van Heurck, as reported from the eastern and central U.S. (Patrick & Reimer 1975), is in need of clarification.