Specific identification of flat forms of the Lemna gibba/L. minor complex on morphological grounds appears to be possible only when the dimensions are > 5.0 x 3.5 mm or/and the number of veins is > 5 (L. gibba), or when the dimensions are < 3.0 x 2.0 mm, the number of veins 3 and/or the width/length ratio < 0.60 (L. minor). A consistent diagnostic character is the ability of L. gibba of turning gibbous when cultivated on EDDHA containing medium.