I found Anabaena aequalis in July 2025 in the Lauchsee Moor in Austria. This cyanobacterium forms unbranched filaments that settled on the wall of the sample container.

A characteristic feature of Anabaena aequalis are the very long, cylindrical akinetes, which are always separated from the heterocysts by several vegetative cells. Additionally, the akinetes have a somewhat rough membrane that stands off from the cells like a bubble (s. fig. 5 a-b). The akinetes are densely filled with highly refractive vesicles. The heterocysts are thick-walled and yellow-green. In my population, the heterocysts were barrel-shaped (s. fig. 6). However, they can also take on an almost oval shape. The vegetative cells are also barrel-shaped. In my population, they were between 6.5-9 µm long. They are blue-green in color.

Anabaena aequalis can be confused with the similar species Anabaena cylindrica and Anabaena inaequalis. However, in Anabaena cylindrica, the akinetes and heterocysts lie directly next to each other, and in Anabaena inaequalis, the width of the vegetative cells varies greatly within the filament.