Desmid of the month
June 2003


Actinotaenium didymocarpum * is a rare, poorly known desmid. In the Netherlands it was reported for the first time in summer 2002. Sampled from a small, shallow, mesotrophic dune pool, in the first instance only vegetative cells were encountered. Originally, those cells — on account of their minute median constriction and the presence of asteroid chloroplasts — were labeled Actinotaenium diplosporum var. americanum forma minus. However, on the basis of the characteristically shaped twin zygospores that were encountered later in the season it was concluded that the algal material in question fully agreed with Actinotaenium didymocarpum as described from Lapland **.

* Penium didymocarpum Lundell 1871, on the basis of its cell wall structure was transferred to the genus Actinotaenium by Coesel & Delfos (1986).

** Possibly, A. diplosporum var. americanum forma minus is identic to A. didymocarpum. Further taxonomic investigations are wanted.


Coesel, P. & A. Delfos, 1986. New and interesting cases of conjugating desmids from Lapland. — Nordic Journal of Botany 6: 363-371.

Vegetative cell of Actinotaenium didymocarpum showing two asteroid chloroplasts.

Cell size (L x B): ca 40 x 15 µm.

Twin zygospore of Actinotaenium didymocarpum with  adhering semicells (cell breadth ca 15 µm).