I have only found Mesotaenium macrococcum once in samples from the Schwemm Moor in Austria. According to Lenzenweger (2003), the species should also occur on moist soils, rocks and between mosses.

The samples from the Schwemm Moor contained colonies with approx. 10–30 cells in a indistinctly layered gelatinous matrix. The cells were quite widely separated from each other in the matrix (s. fig. 1). The most important characteristic of Mesotaenium macrococcum is the plate-shaped chloroplast. (s. figs 4 a-b and 5 a-b). The cells of my population were between 20–36 µm long. This means that the largest cells were significantly longer than in the variety Mesotaenium macrococcum var. minus with 19–26 µm. In the second similar species Mesotaenium chlamydosporum with cells of comparable length (15–33 µm), the plate-shaped chloroplast is clearly divided into two parts in larger cells, which was not the case in my species.