Cells undergoing endoreduplication replicate their genome without mitosis, resulting into a progressive increase of their DNA content. In the plant model species Arabidopsis thaliana, cells undergo endoreduplication in a developmental--‐regulated manner and it is presumed to be a driver of cell expansion and differentiation. Although several regulators of endoreduplication onset have been identified, a major open question is how endoreduplicating cells with a different DNA ploidy level are integrated into a developing organ. We will address this question by focusing on the developing Arabidopsis leaf. At the center of the project lays the construction of a leaf ploidy cartogram using molecular data obtained through advanced cell sorting and microscopic techniques. Subsequently, the obtained map will be used to perturb the endocycle in a tissue--‐dependent manner to understand the role of the endoreduplication process in the growth and development of leaves, both under control and stress conditions.