& Context In response to waterlogging, pedunculate oak is known to develop adventitious roots and hypertrophied lenti-cels. However, to date, a link between these adaptations and the ability to maintain net CO 2 assimilation rates and growth has not been demonstrated. & Aims The aim of this study was to explore the cause–effect relationship between the ability to form morphological adap-tations (hypertrophied lenticels and adventitious roots) and the capacity to maintain high assimilation rate and growth. & Methods The occurrence of morphological adaptations and the parameters of photosynthesis were monitored over 20 days of waterlogging in 5-week-old pedunculate oak seedlings presenting similar morphological development. & Results Based on the development or not of morphological adaptations, the following three categories of responses were identified: development of hypertrophied lenticels and adven-titious roots, development of hypertrophied lenticels alone, and the lack of development of adaptive structures. These categories, ranked in the order given, corresponded to decreas-ing levels of initial net CO 2 assimilation rate growth and photosynthesis parameters observed during waterlogging. & Conclusion We observed a two-way cause–effect relationship between the capacity to form adaptive structures and the assim-ilation rate. Indeed, the initial assimilation rate determined the occurrence of hypertrophied lenticels and growth during stress, and then the development of morphological adaptations en-hanced the ability to maintain assimilation levels during the stress.