Actinotaenium phymatosporumimage © Marien van Westen

Actinotaenium phymatosporum. Note the two asteroid-stelloid chloroplasts each enclosing a globular pyrenoid.

Cell dimensions (L x B): 33 x 15 µm



Desmid of the month
October 2011

Actinotaenium phymatosporum

Actinotaenium phymatosporum (in most floras listed as Penium phymatosporum) may be readily confused with Actinotaenium spinospermum (Penium spinospermum). Both species are characterized by small cell dimensions and a faintly striate cell wall (often the striae are hardly visible). Actually, the striae are made of longitudinal series of closely set cell wall pores, better to be distinguished as the pores are marked by protruding excretion products. Owing to the nature of this cell wall sculpturing both above-mentioned species were transferred from Penium to Actinotaenium (Kouwets & Coesel 1984). Vegetative cells in A. phymatosporum are slightly longer than in A. spinospermum but the main difference is in the shape of the zygospore: irregularly rectangular in A. phymatosporum versus about globose in A. spinospermum. In the Netherlands, A. phymatosporum is known from acidic, oligo-mesotrophic, shallow water bodies. Zygospores are but rarely encountered.

Actinotaenium phymatosporum, dode, lege cel.image © Marien van Westen

Dead, empty cell of A. phymatosporum. Notice faint striation of the cell wall.


Kouwets, F.A.C. & Coesel, P.F.M., 1984. Taxonomic revision of the conjugatophycean family Peniacae on the basis of cell wall ultrastructure. — Journal of Phycology 20: 555- 562.

Actinotaenium phymatosporum, SEM-foto'smouse-over images Hanny Kooijman – van Blokland, © IBED

SEM picture of A. phymatosporum. Notice longitudinal series of cell wall pores.

Mouse over: Detail of apex showing the piling of excreted material around the majority of the cell wall pores.

Actinotaenium phymatosporum, zygosporemouse-over images © Marien van Westen

Zygospore of A. phymatosporum. Notice irregularly shape with rounded, conical protuberances.