Observations on Cosmarium ralfsii var. montanum

As Škaloud et al. (2011) have shown using molecular biology, the sequences of Cosmarium ralfsii Brébisson ex Ralfs 1848 fit into the Micrasterias cladon A (subcladon A1 with M. truncata and M. semiradiata) as it is called there. This study used the strain SVCK 300 of Cosmarium ralfsii, which nomenclaturally means that only the type variety has been transferred to the genus Micrasterias and the forma montanum described by Raciborski in 1885 and later repeatedly found (currently referred to as Cosmarium ralfsii var. montanum (Raciborski) Allorge & Manguin 1941) must continue to be listed in the genus Cosmarium, which is most likely phylogenetically incorrect for this variety! Further molecular biological studies on Cosmarium ralfsii var. montanum are desirable.

A problem in the desmidiological identification literature should be noted. According to Lenzenweger (1999), the variety montanum has significantly smaller dimensions than the type variety, which is expressed in the text and also on Plate 46:

Cosmarium ralfsii var. ralfsii
L.: 90–120 µm, B.: 80–110 µm, I.: 20–25 µm, D.: 50–55 µm.

Cosmarium ralfsii var. montanum
L.: 45–65 µm, B.: 40–55 µm, I.: 16–17 µm, D.: 22–24 µm.

The information on var. montanum may be taken from the secondary literature cited there (W. & G. S. West (1905), Hustedt (1911), Krieger & Gerloff (1962)); Lenzenweger states that he was not able to collect and observe specimens of this variety.

However, in the original description of Cosmarium ralfsii f. montanum Raciborski wrote:
Long. 87 µ; lat. 76 µ; lat. istm 20 µ. Location: Zakopane (High Tatras).

In contrast, Raciborski describes another forma, C. ralfsii f. alpinum, with the following size specifications:
Long. 44; –46; –47; –48; –48; –50 µ.
Lat.    42; –45; –41; –42; –44; –43 µ.
Crass. 22 µ; Lat. isth. 16–17 µ.
Location: Lake Kurtkoviec in the High Tatras.
Apparently four specimens of this forma were found and one specimen of the forma montanum.

The size information in Lenzenweger (1999) is therefore based on a confusion with the dimensions of f. alpinum! In fact, John & Williamson, who found both varieties in Ireland, describe them with the following sizes:
Cosmarium ralfsii var. ralfsii
L.: 117–126 µm, Br.: 101–109 µm, Isth.: 22.5–22.8 µm, Th.: 51–56 µm, L/B: 1.13–1.17
Cosmarium ralfsii var. montanum
L.: 111–115 µm, Br.: 98–99 µm, Isth.: 21 µm, L/B: 1.13–1.16

West & West (1905) also found the following for var. montanum:
Length 87–128 µ, bredth 76–101 µ, breadth of isthmus 20–23 µ.