Cosmarium pseudo-ornatum
Eichler & Gutwiński, 1894
Most likely ID: n.a.
Synonym: n.a.
Sampling location: Schwemm Moor (Austria)
Phylogenetic tree: Cosmarium pseudo-ornatum
Diagnosis:
- semi-cells eliptical or rounded rectangular
- length 28-35 µm, width 26-33 µm
- apices almost flat, sometime slightly convex
- sinus deep, linear closed, laterally widened
- margins of semi-cells granulated
- central field with almost circular arranged warts
- parallel to lateral margins each 2-4 rows of warts
- each two pyrenoids per semi-cell
In July 2025 I found Cosmarium pseudo-ornatum in old samples from the Schwemm Moor. However, there were only very few specimens and they were present in only one sample.
Cosmarium pseudo-ornatum has a beautiful ornamentation of the semi-cells, which makes the species easy to recognize. A central, almost round field of warts is surrounded by lateral rows of warts that are arranged parallel to the lateral margins of the semi-cells. This results in three fields with warts on each semi-cell.
Cosmarium pseudo-ornatum can be confused with the similar species Cosmarium trachypleurum var. minus. However, the central field of this species is characterized by a ring of 6 warts with a central wart in the middle.
More images and information on Cosmarium pseudo-ornatum: Chris & Christine Johnson-Algae outer Hebrides-Cosmarium pseudo-ornatum
Fig. 1 a-b: Cosmarium pseudo-ornatum. L = 36 µm. Two focal planes of a specimen in DIC. Note the central field of warts and the lateral rows of warts parallel to the lateral margins. Obj. 100 X.
Fig. 2 a-b: Cosmarium pseudo-ornatum. L = 36 µm. The same specimen as shown in fig. 1 a-b in brightfield illumination. Obj. 100 X.