120Exploration of Morphological Variation Within the Genus Pediastrum Meyen 1829 (Chlorophyceae, Chlorophyta)

Monographic works on the green algal genus, Pediastrum Meyen 1829 (Chlorophyceae, Chlorophyta), have described species, varieties and forms based on such characteristics as the size and shape of the marginal cells, pattern of cell wall sculpturing and extent of cell wall sculpturing. Depending on the author, the number of taxa assigned to the genus Pediastrum varies. Due to the lack of quantitative value to these characteristics, it has been difficult for other researchers to assign appropriate taxonomy to wild isolates. A molecular phylogeny including multiple strains from both culture collections and wild samples confirms relationships found by previous molecular studies on fewer taxa, in which the family Hydrodictyaceae forms a monophyletic group within the Sphaeropleales, and that the genera Hydrodictyon and Sorastrum are derived from Pediastrum . Hydrodicyton forms a monophyletic clade and consists of three species, H. reticulatum, H. africanum , and H. patenaeforme . Multiple isolates of H. reticulatum reveal little genetic variation between different geographic localities. Inclusion of wild isolates permits a more thorough exploration of morphological variation within the genus Pediastrum , and what characters may be taxonomically informative, particularly in the species P. boryanum and P. duplex . Wild isolates sampled from different areas also offers information regarding geographic variation and potential morphological convergence.