Abstract: Turion formation is poorly studied in all of the Wolffia species and only narrow studies have been done. In this study details of Wolffia columbiana ecology and physiology are related to anatomy and histochemistry. We used a combination of histochemistry and a new method of pressing tissue into one focal plane to reveal anatomical features that are not visible using conventional methods. Previously unknown organs, wax coated substomatal cavities, are described which play a crucial role in Wolffia ecology. Tank experiments were used to determine the behavior of Wolffia columbiana plants in response to light and dark conditions. A physiological mechanism for transition between an invasive floating population and dormant benthic population using oxygen floatation is described, which involves Wolffia columbiana behaving like a small bathyscaphe. This mechanism is combined with accumulation of large stores of starch and is an adaptation to colonization and overwintering.