Cosmarium
Desmidiaceae –
Archaeplastida

Observations on Cosmarium pseudowillei (*)

Protisten / Protisten.de – created by Wolfgang Bettighofer / Algae green-colored (2: Desmidiaceae): Cosmarium / Cosmarium pseudowillei

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Cosmarium pseudowillei Kouwets 2025

Most likely ID: n.a.

Basionym: n.a.

Add’l Synonyms: n.a.

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(*) A competing taxon for this algal form was described by Krieger & Gerloff (1969) and is also published in Lenzenweger (1999);
see the discussion below:

Cosmarium quadratum var. willei (Schmidle) Willi Krieger & Gerloff 1969

Most likely ID: n.a.

Basionym: Dysphinctium quadratum var. willei Schmidle 1893 (as “Disphinctium”)

Add’l Synonyms: Cosmarium quadratum f. willei (Schmidle) West & G.S.West 1908
Cosmarium quadratum f. majus Nordstedt 1888

Sampling date 06/2024. Scale bars indicate 25 µm.

Five images. Optical journey into the cell.

First:	Synoptic representation of the cell with finely dotted cell wall decoration. This dots are cell wall pores through which the protective mucilage is deposited.
Second and third:	Two optical cross-section showing lobes of the chloroplasts.
Fourth:	Nucleus with wings of the chloroplasts.
Fifth:	Nucleus with the four pyrenoids.

Please click on < or > on the image edges or on the dots at the bottom edge of the images to browse through the slides!

Place name: Wetland at the Pillersee (Tyrol, Austria)
Latitude: 47.531785 Longitude: 12.573095

Microscope Zeiss Universal, camera Olympus OM-D M5 MKII. DOF images.

Sampling date 06/2024. Scale bars indicate 25 µm.

Four images. Optical journey into the cell. Same cell as above, but higher objective aperture.
The circular pattern on the cell wall is caused by a slight contusion caused by the coverslip pressure.

First:	Synoptic representation of the cell with finely dotted cell wall decoration.
Second:	Optical cross-section showing lobes of the chloroplasts.
Third:	Nucleus with pyrenoids.
Fourth:	Pyrenoids.

Please click on < or > on the image edges or on the dots at the bottom edge of the images to browse through the slides!

Place name: Wetland at the Pillersee (Tyrol, Austria)
Latitude: 47.531785 Longitude: 12.573095

Microscope Zeiss Universal, camera Olympus OM-D M5 MKII. DOF images.

The relationship between the two taxa Cosmarium quadratum var. willei (Schmidle) Willi Krieger & Gerloff 1969 and Cosmarium pseudowillei F.A.C. Kouwets 2025

The alga first described by Nordal Wille in 1879 as an unnamed form of Cosmarium quadratum, and named Disphinctum (sic!) quadratum var. willei by Schmidle in 1893, referring to Wille’s publication, with a notched, V-shaped opening sinus, certainly represents a different species than what, for example, Lenzenweger showed in Plate 51, Fig. 35a, who refers to Krieger & Gerloff 1969.

First, the illustrations in Schmidle (1893), Fig. 1 and 2:

Cosmarium quadratum var. willei sensu Schmidle/Wille

In contrast, Fig. 35a in Lenzenweger (1999) shows for Cosmarium quadratum var. willei:

Cosmarium quadratum var. willei sensu Krieger&Gerloff/Lenzenweger

For the latter form, which differs significantly from Wille’s graphics, Kouwets introduced the taxon Cosmarium pseudowillei in 2025.

Coesel & Meesters, on the other hand, believe that all described varieties and forms of Cosmarium quadratum only contain minor variations in form, which often only apply to half-cells and therefore do not justify separate taxa.

References

Coesel, P. F., & Meesters, K. J. (2023). Desmids of the Lowlands. 2nd revised and extended edition. KNNV Uitgeverji, Zeist, the Netherlands.

Kouwets, F. A. C., (2025). European flora of the desmid genus Cosmarium, Part 1 Text and Part 2 Plates. 24bookprint, Rotterdam.

Krieger, W., & Gerloff, J. H. (1969). Die Gattung Cosmarium: Folge 3-4. J. Cramer, Weinheim.

Lenzenweger R. (1999). Desmidiaceenflora of Austria, Part 3. Schweizerbart, Stuttgart.

Schmidle, W. (1893). Beiträge zur Algenflora des Schwarzwaldes und der Rheinebene. Naturforschende Gesellschaft zu Freiburg i. B.

Wille, N. (1879). Ferskvandsalger fra Novaja Semlja samle de af Dr. Kjellman paa Nordenskiölds expedition 1875. PA Norstedt & Söner.

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