Abstract text: Potamogeton nodosus, an aquatic angiosperm, exhibits heterophylly, with two morphotypes depending on leaf position within the water column. We performed the sequencing and the assembly of the genome as well as a transcriptomic study to compare gene regulation between the two morphotypes. This first study highlighted a significant involvement of cell wall–related genes. We then focused on the cell wall by generating the first leaf cell wall proteome for this species, complemented by an immunohistological atlas of selected cell wall polysaccharides and glycoprotein epitopes. The cell wall proteome revealed a notable overrepresentation of proteins involved in polysaccharide modification, including glycoside hydrolases, pectin methylesterases, and TRICHOME BIREFRINGENCE-LIKE proteins. Additionally, we identified proteins enriched in submerged leaves which are associated with carbon-concentrating mechanisms, an essential adaptation in many aquatic plants. Consistent with these findings, immunolabeling-based spatial profiling revealed localized pectin epitopes with variable (i) homogalacturonan methyl- and acetyl-esterification patterns and (ii) arabinan epitopes distribution. Collectively, these results suggest a stiffness gradient across tissues, with more rigid cell walls in aerial-facing regions and increased compliance in water-exposed tissues. This plasticity likely underpins the functional adaptation of the plant to contrasted aerial and submerged conditions.