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), Simmelried

 

Phylogenetic tree: Cosmarium granatum

 

Diagnosis: 

  • 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
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) and in the Simmelried in May 2025. 

 

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. figs. 1 a-b and 3). The cell wall of Cosmarium granatum is quite thick in relation to the cell size. It is finely granulated, without warts or tubercles.

Cosmarium-granatum

Fig. 1 a-b: Cosmarium granatum. L = 42 µm. Two focal planes of a specimen found in May 2025 in the Simmelried. Obj. 100 X.

Cosmarium-granatum

Fig. 2 a-b: Cosmarium granatum. L = 42 µm. The same specimen as shown in fig. 1 a-b in brightfield illumination. Obj. 100 X.

Cosmarium-granatum

Fig. 3: Cosmarium granatum. L = 43 µm. A second specimen found in May 1996 in the Tettermoor (Austria). Obj. 100 X.

Download PDF