Cosmarium orthostichum Lundell, 1871
Most likely ID: n.a.
Synonym: n.a.
Sampling location: Schwemm Moor (Austria)
Phylogenetic tree: Cosmarium orthostichum
Diagnosis:
- semi-cells ellipsoid, apices flat, sides convex
- length 36–37 µm, width 31–33 µm
sinus deep, laterally widened
cell wall with transverse rows of warts - paired warts near central field
- one chloroplast with one pyrenoid per semi-cell
So far, I have only found a few specimens of Cosmarium orthostichum in the Schwemm Moor in Austria. Lenzenweger (1999) also reports that this alga occurs only sporadically.
The essential characteristic of Cosmarium orthostichum is the paired, sometimes even triple, warts in the central field of the semi-cells (s. fig. 1 c). However, this feature can only be recognized at high magnification. The size seems to lie within a very narrow range. Lenzenweger gives a length of 36–37 µm, while my specimens were mostly 38 µm long. This therefore also seems to be a fairly constant characteristic of Cosmarium orthostichum.
Fig. 1 a-c: Cosmarium orthostichum. L = 38 µm. Three focal planes of a slightly squashed specimen. Note the paired warts in the central field of the semi-cells (arrows). Obj. 100 X.
Fig. 2 a-c: Cosmarium orthostichum. L = 38 µm. The same specimen as shown in fig. 1 a-c in brightfield illumination. Obj. 100 X.