Closterium ehrenbergii is a very common representative of the genus Closterium. In addition to the impressive size of usually over 400 µm, the pyrenoids scattered in the chloroplasts are the main identifying feature (s. figs. 2 and 3). In all other species of Closterium, except Closterium lunula, the pyrenoids are arranged more or less along the longitudinal cell axis. The cell shape of Closterium lunula, however, is almost straight and less curved.

The cell wall of Closterium ehrenbergii has a very fine striation (s. fig. 4). This can be more or less pronounced. In the older literature, the subspecies Closterium ehrenbergii var. malinvernianum is defined as having a more pronounced striation. However, Lenzenweger (1996) considers this to be an uncertain characteristic, which is why the delimitation of a subspecies does not appear to be justified. Although the specimens of my population showed a fine but clearly visible striation, I stick to the identification Closterium ehrenbergii.