Actidesmium is a small genus of green algae in the family Characiaceae.

[1] Actidesmium consists of microscopic colonies of numerous cells.

[2] Actidesmium reproduces by zoospores formed by successive division.

[1] The two differ in the size and shape of their cells, the latter being smaller and globose.

[4] Actidesmium has been reported from freshwater habitats in North America and Europe, and is rare.