Cosmarium granatum

(Brébisson ex Ralfs, 1848)

Most likely ID: n.a.


Synonym: Ursinella granata, Euastrum granatum, Cosmarium granatum f. pentagonum


Sampling location: Wollmatinger Ried, Tettermoor (Austria)


Phylogenetic tree: Cosmarium granatum



  • semi-cells trapezoidal or triangular with broadly rounded corners
  • basal part of the half cells sometimes with parallel sides
  • length 20–48 µm, width 13–31 µm
  • sinus narrow, slightly dilated to the istmus
  • cell wall finely granulated, thickened at apices
  • one pyrenoid per semi-cell
Cosmarium granatum

I first found Cosmarium granatum in December 1994 in a shallow pond in the Wollmatinger Ried. In May 1996 I found further specimens in samples from the Tettermoor (Austria). After that I have no evidence of further finds.


I recognize Cosmarium granatum by the almost triangular shape of the half-cells, whereby the corners are always broadly rounded. Sometimes the sides are angled again just above the sinus (s. fig. 2). The cell wall of Cosmarium granatum is quite thick in relation to the cell size. It is finely granulated, without warts or tubercles.


Fig. 1 a-b: Cosmarium granatum. L = 39 µm. Two focal planes of a specimen found in December 1994 in the Wollmatinger Ried. Obj. 100 X.


Fig. 2: Cosmarium granatum. L = 43 µm. A second specimen found in May 1996 in the Tettermoor (Austria). Obj. 100 X.