Actinotaenium species lacks ornamentation and are for the most part described on basis of their size and outline. Close examination revealed however that specimen with roughly the same outline can vary significantly in cell wall structure (pores and pore fields) and in the structure of the chloroplast. Especially when the original descriptions are poor, an amount of species will be constantly under discussion and that will not end until the species of this genus are thoroughly examined, particularly with the use of SEM-microscopy.