Protococcus

Protococcus

 or Pleurococcus

Genus of green algae. Popularly called moss though not actually classified as such, it is found as a thin, green covering on the moist, shaded side of trees, rocks, and soil. The spherical cells, either solitary or clumped together forming short false filaments, have heavy cell walls that protect them against excessive water loss. Each cell contains a large dense chloroplast. The position of Protococcus in classification systems is uncertain.