Image © Frantisek Hindák
Cell size (L x B): ca. 25-40 x 10 µm
The genus Mesoatenium belongs to the saccoderm desmids in which the cell wall, contrary to the placoderm desmids, consists of but one single piece (no semicells to be distinguished). Representatives of this genus may develop, next to their green chloroplast pigments, also a purplish pigment, colouring cell sap pale purple to reddish-brown. Most likely this purplish pigment protects cell content against damage by UV radiation for it can be found in particular in snow algae living in high mountains and arctic regions.
The presence of this pigment in Mesotaenium-species occurring in more temperate climatic regions may be explained from the fact that Mesotaenium species use to grow atmophytically on bare substrates which are exposed to high light intensities.The herewith reproduced purple-reddish cells of Mesotaenium endlicherianum were encountered on the bank of a sand-pit near Bratislava, Slovakia. For comparison, also Mesotaenium cells are figured in which the purplish pigment is lacking.