I have only found Planktothrix mougeotii in the Bussenried so far. A typical characteristic of the genus Planktothrix are the solitary filaments. They are on average 300–500 µm long. In addition, the cells of Planktothrix contain vacuoles filled with gas, which often makes the filaments appear blackish in transmitted light. Within the filaments there are often segments of cells that do not contain gas vacuoles (s. fig. 4 a). This is another characteristic of the genus Planktothrix.

The differentiation of the species is mainly based on the diameter of the filaments and the shape of the apices. In Planktothrix mougeotii the filaments should be 5.5–7.5 µm thick. The apices of the filaments are not or only slightly tapered and the terminal cells are rounded (s. figs 2 a-b and 3). The crosswalls show no or only slight constrictions.