Comparative physiology,biochemistry, and the taxonomy ofChlorella (Chlorophyceae)

According to biochemical and physiological characters, 77 strains ofChlorella were assigned to 12 taxa. The characters used are presence or absence of hydrogenase, formation of secondary carotenoids under nitrogen-deficient conditions, liquefaction of gelatin, products of glucose fermentation, ability to reduce nitrate, thiamine requirement, acid tolerance, salt tolerance, thermophily, and base composition of DNA (GC content). On the other hand, certain nutritional characters, i. e., utilization of organic carbon and nitrogen compounds, were found to be more or less strain-specific, highly variable, and therefore unsuitable for taxonomy.Presented at the symposium Speciation and the Species Concept during the XIIth International Botanical Congress, Leningrad, July 8, 1975.