Light micrograph (DIC) of the disc-like colony of cells formed by the green alga, Pediastrum sp. Pediastrum is a type of freshwater colonial algae. The colony comprises a central cell surrounded by concentric rings of cells. Cells (with chloroplast) and cell walls are shown with some cells having visible pyrenoids (circular spots). The pyrenoid's function is to promote photosynthetic CO2 fixation. Magnification: x1400 when printed at 10 centimetres wide at its longest edge.