Guide to Navicula

Valves of Navicula tend to be elliptic to broadly-lanceolate in outline. Valve ends may be capitate, acute, rounded, or not expanded. The central sternum is thickened, and that thickening may be somewhat asymmetric. Pseudosepta may be present, or absent. The raphe is straight and filiform, or lateral in some species. The proximal raphe ends are slightly deflected to one side. The central area may be expanded, but the silica is not thickened into a fascia.

A defining character of Navicula is the lineate areolae, or lineolae.

During the mid-1900's, primarily through the work of Hustedt, Navicula became a genus that contained a large number of unrelated lanceolate, biraphid species. Many of these unrelated species have been separated into new genera or replaced into the older, originally described genera. Note that many species remain within Navicula that do not belong to Navicula in the strict sense.