Very little is known about the diversity and distribution of freshwater unicellular coccoid green algae. The simple morphology and small size of these organisms make reliable identification extremely difficult. Current hypotheses suggest that species of coccoid algae are widely distributed, opportunistic organisms that are always present in aquatic systems. These hypotheses are based on the assumption that phytoplankton communities include only one or a few species of coccoid algae. We examined the diversity and distribution of green-colored autosporic coccoid algae in Itasca State Park in Minnesota and Arrowwood National Wildlife Refuge in North Dakota using molecular techniques and light microscopy. Our preliminary results indicate a higher level of diversity of coccoid green algae than has been reported in regional floras. Contrary to current hypotheses, communities of coccoid green algae vary among the different lakes.

Key words: Chlorella, Chlorophyceae, coccoid algae, community structure, Trebouxiophyceae