So far, I have only found Euastrum crassum in the Ibmer Moor (Austria) and in the Schwemm Moor (Austria). In these locations, the species occurs in large numbers in some places.

Euastrum crassum is easily recognizable by its more or less trapezoidal semi-cells. The apical lobe is divided by a deep incision, which is closed at the top. The cell wall is clearly thickened at all protuberances. Each half-cell has three basal protuberances near the isthmus, which can sometimes touch at the cell equator. Approximately in the middle of each semi-cell there is a large pore that is clearly visible (s. fig. 2). Otherwise, the cell wall appears finely granulated due to many smaller pores. The chloroplasts in the semi-cells each contain a few scattered pyrenoids.