Within the GeeDAFF team which is part of the EFNO unit belonging to INRAE Val de Loire, I participated in research on the conservation of the genetic resources of native elms (smooth elm, field elm and mountain elm ). The latter is necessary because elms are threatened on the one hand by the destruction of their habitat (riverine trees) as is the case for smooth elm and on the other hand, by a disease, the Dutch elm disease caused by a fungus and transmitted by Scolytes which mainly affects field elm and mountain elm. These factors threaten populations and therefore the genetic diversity they contain, which ensures the long-term sustainability of these species. In order to protect these vulnerable populations, Conservatory Units (UC) were set up to conserve the genetic resources of elm trees in a natural environment (in-situ conservation) or not (ex-situ conservation). The ‘Talonet’ conservatory located in the area of bars is an ex-situ conservatory which takes the form of low hedges. Clones from all over Europe are kept there. Many tasks were entrusted to me during my internship (a bibliographical study on the regeneration of smooth elm in natural environments, updating data from the Talonet conservatory, harvesting samaras in the field, labeling ...) but I chose to develop one of them: The search for discriminating criteria between native elm species. During a field trip, the GeeDAAF team had difficulty differentiating smooth elm from field elm. My work consisted in harvesting elm twigs on the 'Talonet' conservatory to then observe under a microscope (magnification between x50 and x200) the buds of the different species in order to find differentiation criteria applicable in the field by the members of the the team. In addition, using different flora and a database of photos of leaves of the clones present in the conservatory, I gathered discriminating criteria on the leaves of these three species. All of these criteria were then brought together and formatted on a single document to allow team members and their collaborators to differentiate these species.