Gomphonema vibrioides

Valves are narrowly linear-lanceolate, with a bluntly rounded headpole. The footpole is less broad than the headpole. Valves are inflated or tumid in the middle, a feature more more pronounced in larger valves. The axial area is straight, moderately large, and wider at the central valve than at the apices. Striae are punctate, coarse, and radiate near the center. There is an isolated stigma next to a shortened median striae (only slightly shortened opposite stigma) along the central area. Within a population, the position of the stigma varies in distance from the central striae. The central area is small and transapically linear, with shorter striae on either side.

Morphological variation of this taxon is recorded in populations of the United States (Morales 2001). In the Florida Everglades, specimens intergrade across valve length between G. vibrioides and G. intricatum var. vibrio (sensu Fricke in Schmidt 1874-1959, T: 235/10-12).

Note that G. intricatum var. vibrio sensu Fricke  is considered a subjective synonym of G. vibrioides (Reichardt and Lange-Bertalot 1991). However,  G. intricatum var. vibrio sensu Fricke includes several morphotypes with a great deal of morphological variation (Morales 2001). Also considered part of this species complex is Gomphonema intricatum var. vibrio (Ehrenb.) Cleve 1894 which is an objective synonym for G. vibrio Ehrenberg 1843. The unresolved complexity of this group would benefit from further work.