I find Tetradesmus lagerheimii in large numbers in the plankton of the pond of the waste disposal company Constance. There it seems to have good growth conditions, because the size of the coenobia in my polulation are at the upper end of the range given for this species.

The species was originally described as Scenedesmus acuminatus by Lagerheim, but was placed in Tetradesmus by Wynne & Guiry in 2016. It is possible to confuse Tetradesmus lagerheimii with the similar species Tetrademus dimorphus (Syn. = Scenedesmus dimorphus). However, Tetradesmus lagerheimii has much longer, tapered cell ends and the outer cells are more strongly, arcuately curved in Tetradesmus lagerheimii (s.  fig. 1).

The single-cells in the coenobia in my population were on average 50 µm long and clearly alternatingly arrganed. This can be seen in the arrangement of the pyrenoids in the coenobia, which are arranged in a zig-zag pattern rather than in a line (s.  fig. 1). Many of the single cells in the coenobia had 2 nuclei (s. fig. 1). The literature does not mention the nuclei in any way, but I found this circumstance astonishing. I found the surface of the cells to be smooth as described in the literature, but I could see a delicate but distinct spiral striation at the cell ends (s. fig. 2), which is not mentioned in the literature.