Ten rare filamentous cyanobacterial oscillatorialean morphospecies, recorded in plankton of freshwater water bodies in tropical and subtropical South America, mainly in São Paulo State, Brazil, are described in this article. Four morphospecies from the genera Romeria, Arthrospira, Planktothricoides and Hormoscilla are not identifiable according to literature, and they are described as new for science.
Cyanobacteria; new species; phytoplankton; taxonomy
