Cosmarium elegantissimum Lundell, 1871
Most likely ID: n.a.
Synonym: Pleurotaeniopsis elegantissima
Sampling location: Schwemm Moor (Austria)
Phylogenetic tree: Cosmarium elegantissimum
Diagnosis:
- semi-cells cylindrical with broadly rounded apices
- cell circular in apical view
- length 85–95 µm, width 30–38 µm
- cell wall covered with round warts in 8–9 transverse rows
- warts on cell wall paired
- one chloroplast and one pyrenoid per semi-cell
- one branched chloroplast per semi-cell
Cosmarium elegantissimum is described by Lenzenweger (1999) as a species that occurs only sporadically in alpine bogs. I have found it only once in June 2025 in the Schwemm Moor in Austria.
A characteristic feature of Cosmarium elegantissimum are the almost cylindrical semi-cells with broadly rounded apices. The cell wall of each semi-cell is covered with 8-9 transverse rows of double warts. The few specimens I found had a length between 72 and 78 µm and were thus somewhat smaller than the 85–95 µm given by Lenzenweger.
The similar species Cosmarium tessellatum is about twice as large, with a length of 130–160 µm, and has more than 10 transverse rows of warts.
Fig. 1 a-b: Cosmarium elegantissimum. L = 74 µm. Two focal planes of a specimen found in June 2025 in the Schwemm Moor. Note the paired warts (arrows) covering the cell wall in 9 transverse rows per semi-cell. Obj. 100 X.
Fig. 2 a-b: Cosmarium elegantissimum. L = 74 µm. The same specimen as shown in fig. 1 a-b in brightfield illumination. Obj. 100 X.