Pediastrum duplex

Pediastrum duplex is a species of fresh water green algae in the genus Pediastrum. It is the type species of the genus Pediastrum.

Pediastrum duplex forms nonmotile coenobia (colonies) with a fixed number of cells. These coenobia are flat and have a circular shape. The colonies usually contain 8 to 32 cells, with examples of 4, 64 or 128 occurring rarely. Colonies have holes between the cells; the holes are smaller in diameter than the cells. The cells are polygonal, distinctly rectangular in outline with concave sides. The outer cells of the coenobium have two triangular lobes that are longer than the cell body. At the tip of the lobes are very short rosettes that may also have fine bristles. The cell wall is usually smooth, but may sometimes have a distinct sculptured texture. It reproduces by forming autocolonies asexually, although sexual reproduction has also been observed.

Pediastrum duplex is a very common component of the freshwater phytoplankton, and has a cosmopolitan distribution. Because the cell wall is resistant to decay, the cell wall has been found in Holocene lake sediments.

Infraspecies
Because Pediastrum duplex is very variable, many infraspecific taxa have been named. A partial list is included below:

Pediastrum duplex brachylobum

Pediastrum duplex clathratum

Pediastrum duplex cohaerens

Pediastrum duplex duplex

Pediastrum duplex f. denticulatum Isabella & R.J. Patel

Pediastrum duplex gracillimum

Pediastrum duplex regulosum

Pediastrum duplex reticulatum

Pediastrum duplex rotundatum

Pediastrum duplex var. asperum

Pediastrum duplex var. clathratum (A.Braun) Lagerheim, 1882

Pediastrum duplex var. convexum W. Krieger

Pediastrum duplex var. cornutum

Pediastrum duplex var. gracillimum W. West & G.S. West

Pediastrum duplex var. irregulare G.R. Hegde & K. Somanna

Pediastrum duplex var. longicorne W. Krieger

Pediastrum duplex var. reticulatum Lagerheim, 1882

Pediastrum duplex var. rugulosum Raciborski

Pediastrum duplex var. subgranulatum Raciborski

One variety, Pediastrum duplex var. gracillimum, has been shown to be not closely related to Pediastrum duplex sensu stricto. It differs by having cells with narrower lobes and comparatively larger gaps between cells in the colonies. This variety has been split off as a new genus, named Lacunastrum with Lacunastrum gracillimum as its sole species.