[1] It is an extremely rare genus; it has only been recorded once,[1] as freshwater phytoplankton from its original locality in the Bohemian Forest region of the Czech Republic.

[2] Marthea tetras consists of cells in colonies of four in a cross shape.

Cells are spindle-shaped, with the base attached to a central mass of mucilage, while the apex of the cells are pointed.

Cells contain one nucleus and a single, parietal chloroplast with one pyrenoid.

Unusually, the autospores show amoeboid movement for some time, before settling in their usual shape and being released from the sporangium.