Staurastrum furcatumImage © Marien van Westen

Cell of Staurastrum furcatum in a single focus plane showing but 2 (out of 3) median processes and 2 (out of 6) apical ones. Notice furcate spines (tip of the processes).

Cell dimensions (L x B, including spines): ca 35 x 30 µm

 

 

Desmid of the month
October 2014

Staurastrum furcatum

As its name indicates, Staurastrum furcatum is marked by furcate spines. It can, however, be confused with a number of other species with a suchlike ornamentation. As compared with those species, St. furcatum can be recognized by the number of processes (in triradiate semicells an apical whorl of 6 and a median whorl of 3) as well by its cell wall granulation pattern (confined to the semicell angles, not seldom completely wanting). In the Netherlands, St. furcatum is of occasional occurrence in acidic, oligotrophic bogs and moorland pools. Zygospores (globular, furnished with long, furcate spines) are but seldom encountered.

Staurastrum furcatum, zygospore
Image © Marien van Westen

Zygospore of St. furcatum. Notice long, furcate spines.

 

Staurastrum furcatum in apical view
Image © Marien van Westen

Empty semicell of St. furcatum in apical view. Notice 3 x 2 apical processes and 1 x 3 median processes (vaguely pictured).

Staurastrum furcatum var. aciculiferum
Image © Alfed van Geest

St. furcatum var. aciculiferum. In this variety, the apical processes are reduced to short, simple spines.

Staurastrum furcatum var. aciculiferum, empty cell
Image © Alfred van Geest

Empty cell of St. furcatum (var. aciculiferum) showing some concentric series of small granules at the semicell angles (flanks of the semicells are without such ornamentation).