In Southern Brazil the great diversity of bees is due to the richness of ecosystems in the region and when studies attribute the processes for identification of the floral resources used by bees we can get important steps for the elaboration of management and conservation plans of the species involved. Based on this setting and considering that the study area is a "várzea" (swamp) with a large concentration of flowers of Ludwigia sericea and Ludwigia peruviana, important sources of resources for bees, the aim of this study was to find out about the floral visitor bees and through palynological studies and interaction networks, understand the role of these plants as providers of  pollengrains to bees and how the bees interact with them and other plants, also found in this habitat. Ludwigia sericea, Ludwigia peruviana and the other plant species are presented as generalist in the interactions with the bee species, and the same occurs for most of the bee species in relation to these plants. Generalist bee species (Bombus pauloensis, Apis mellifera, Augochlora amphitrite and Melissoptila paraguayensis) tend to be more abundant and more resistant to disturbances than the specialist species. It was the first time that Plebeia emerina, Centris varia, Mourella caerulea and Augochlorella ephyra were recorded on the Ludwigia flowers in Brazil. Based on the results presented in this study, these plants are important for maintaining the bee community in the region of the Atlantic Forest in Southern Brazil, because they provide resources (nectar and pollen) to bee species that only occur in this region.