image: © Henk Schulp
In the Netherlands, Micrasterias thomasiana is one of the commoner representatives of the genus Micrasterias. Usually finds refer to its variety notata, characterized by a less pronounced cell wall sculpture. For instance, in var. notata, wing-shaped protuberances at the base of the semicell on both sides of the isthmus are highly reduced. The nominal variety of M. thomasiana, in which those protuberances are well developed (see pictures) appears to prefer a somewhat more acideous and less nutrient-rich habitat (as compared to var. notata) and, in the Netherlands, is rather rare. According to Ruzicka's (1981) flora, in all mid Europe M. thomasiana is rather common. Yet there seem to be exceptions. In a large (640 square km) reserve in western Bohemia, rich in desmid species, Trojankova (2002) found M. thomasiana to be a rare, endangered species.
Ruzicka, J., 1981. Die Desmidiaceen Mitteleuropas. Band 1, Lief. 2. - E. Schweizerbart, Stuttgart.
Trojankova, K., 2002. Desmids from the Slavkovsky Les preserved area in western Bohemia, Czech Republic. - Abstracts 4th Symposium Biology and Taxonomy of Green Algae, Smolenice, p.86.