Euastrum dubium
Image © Alfred van Geest

Euastrum dubium (var. dubium). Notice trapeziform semicells with undulate lateral sides and a truncate apex with a distinct median incision.

Cell dimensions (L x B):  28 x 19 µm

 

 

Desmid of the month
April 2018

Euastrum dubium

Eu. dubium is a small-sized Euastrum species characterized by trapeziform semicells that are on each side provided with a lateral lobe just in between the basal and the apical lobe giving rise to an undulate appearance. Lobes are mutually separated by rather shallow, wide incurvations. The truncate semicell apex, on the contrary, is marked by a sharp median incision. Cell wall ornamentation is in the form of a variable number of locally grouped, rounded tubercles, granules, pits or furrows. Zygospore globose, furnished with rather short, stout spines. In the Netherlands, Eu. dubium is of rather rare occurrence in meso-oligotrophic fen hollows and moorland pools. Zygospores were only recently encountered.

Mouse over images © Koos Meesters

Zygospore of Euastrum dubium (var. ornatum). Notice short, stout spines.


Image © Alfred van Geest

Euastrum dubium var. ornatum, differing from the nominate variety by a deeper median apical incision and a more prominent cell wall sculpturing (notice, e.g., granules at the apical angles).


Image: Hanny Kooijman née Van Blokland © IBED

SEM picture of Euastrum dubium (var. ornatum) showing details of cell wall sculpturing.