Staurastrum alternans in frontal view. Notice finely granulate cell wall, widely open sinus and broadly rounded angles.

Cell dimensions (L x B): 23 x 25 µm

S. alternans in apical view. Notice semicell lobes alternating with those of the underlying semicell.



Desmid of the month
November 2013

Staurastrum alternans

S. alternans belongs to a group of Staurastrum species the cell wall of which is evenly beset with small granules. The species under discussion owes its name to the fact that the angles of one semicell usually alternate with those of the other. In frontal view, semicells are subelliptic-subtriangular in outline with broadly rounded lateral angles. The cell sinus is widely open. In apical view, semicells are triangular with concave sides and rounded angles. In the Netherlands, S. alternans is rather common in slightly acidic, mesotrophic pools.

SEM picture of a dividing cell of S. alternans. Notice that the cell wall granules are arranged in regular, concentric rings around the angles.