Oscillatoria is a genus of filamentous cyanobacteria. It is often found in freshwater environments. Its name refers to the oscillating motion of its filaments as they slide against each other to position the colony to face a light source. Oscillatoria uses photosynthesis to survive and reproduce. Each filament of Oscillatoria consists of a row of cells called a trichome. The tip of the trichome oscillates like a pendulum.

Reproduction takes place asexually by fragmentation. Usually the filament breaks into a number of fragments called hormogonia. Each hormogonium consist of one or more cells and grows into a filament by cell division in one direction. Hormogonia has capacity for locomotion.

As a result of recent genetic analyses, several new genera were erected from this genus, e.g. Tenebriella.

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