AbstractNatural hybridization mediated by pollen flow has been considered as an important factor to drive speciation in Rhododendron, one of the largest genera within alpine plants. The diversity of Rhododendron species is centered in southwestern China, yet the potential role of interspecific pollination in natural hybridization has not been empirically examined in this area. Here we investigated the flowering period and floral visitors, and conducted a series of pollination experiments to examine breeding systems and hybrid compatibility within four Rhododendron which are frequently sympatric in Yunnan Province. Rhododendron delavayi and R. decorum are clearly distinct by their morphological traits, but the putative hybrids R. agastum and R. irroratum are morphologically between the other two species. We observed that R. delavayi flowered from the beginning of March to the end of May, R. agastum and R. irroratum flowered from the beginning of March to the beginning of April, and after their flowering periods ended, R. decorum began to flower until the end of May. The anthesis of single flowers of the four Rhododendron species was almost one week. The floral visitors belong to the Hymenoptera and Diptera Orders, and Apis cerana cerana visited all of the four Rhododendron species. We found that R. delavayi, R. agastum and R. decorum are self-incompatible, but not R. irroratum. No breeding barrier between any of the four species was detected by artificial pollination, and the hybrid seeds were fertile. The hybrids between four species showed equivalent fitness to their par-ents. We suggest that the role of potential interspecific pollination is essential to hybrid speciation and evolu-tion of Rhododendron species.