Fifteen strains of subgenus Lemna, collected in ponds and ditches in the western part of The Netherlands, strain G3 (previously described as Lemna gibba) and strains 6573 and F (previously described as Lemna minor) were aseptically cultured on M-medium in the presence and absence of EDDHA. When cultivated on EDDHA medium the strains showed a marked variation in the degree of gibbosity, whereas in the absence of the chelate all strains were more or less flat. The strains could be divided into two groups as far as the degree of gibbosity in the presence of EDDHA was concerned. There were no consistent differences in morphology between the two groups if cultured on the nutrient medium devoid of EDDHA. In the light of the present investigation distinction between Lemna gibba and Lemna minor seems not always possible.