In West Africa, alliance built between researchers, policy makers and fondation aspire to enhance agricultural productivity, food security and rural well-being of 33 million smallholder farming households. In order to, they bred and released quality-improved certified seed through a network of agro-dealers and regulatory frameworks. Supported at the expense of peasant seed used and shared for ages by farmers, this process is likely to impact agroecosystem's resilience and crop diversity. For now, certified and peasant seed coexist within farmer's field. However, coexistence modalities between certified and peasant seeds in farmer seed network are still un- appreciated. By combining quantitative and qualitative analysis, we present a study of millet seed circulation according to their certified or peasant origin. The aim is to identify the coexis- tence modalities in seed exchange between farmers. From surveys of 79 people in the Koungheul region of Senegal, we identified several levels of coexistence, both in the perceptions of varieties by farmers and in networks mobilized for seed supply. Based on our comparative analysis, our results suggest that origin of seed shapes farmer seed networks. The acquisition of certified seeds from agro-dealer also modifies the context and modalities of exchange by inducing their social isolation and limiting self-production. Nonetheless, after the harvest, certified and peasant seed are commingled and embedded into an open and complex social network involving multiples ac- tors. Our results provide a better understanding of seed exchange networks between farmers, by characterizing the structure, the scope and modalities of exchange of certified seed. This study highlights a gap between agricultural policies and local seed management by farmers, results that could feed into the reflections on the governance of plant genetic resources.