Chiang Mai Journal of Science

 Pediastrum spp., one of the most beautiful phytoplankton, are green algae belonging to the Division Chlorophyta. This research aims to study the diversity of Pediastrum spp. in terms of morphology and cell wall ultrastructure which are recognizable under light microscope and scanning electron microscope. The water quality based on certain physical and chemical parameters at 66 from various freshwater resources in Thailand was also investigated. A total of 60 taxa consisting of 26 species were found and 22 taxa were newly recorded from Thailand. Pediastrum duplex var. duplex Meyen, P. tetras (Ehrenberg) Ralfs and P. simplex var. simplex Meyen were the dominant species. Three species, namely P. alternans Nygaard, P. asymmetricum T.Yamagishi & E.Hegewald and P. privum (Printz) E.Hegewald are considered rare in Thailand.  An evaluation of the water quality from all sampling sites based on the trophic status indicated that these water resources could be classified into 4 statuses as oligo-mesotrophic, mesotrophic, meso-eutrophic and eutrophic statuses. Most of the sites were found to be meso-eutrophic status.  The species which could assess the water quality as being  meso-eutrophic status were P. duplex var. duplex Meyen, P. tetras (Ehrenberg) Ralfs and P.simplex var. simplex Meyen.