The evolution of full heterotrophy is a fascinating topic in plant evolution, with recent studies suggesting that partial mycoheterotrophy (mixotrophy) serves as a transitional stage toward full mycoheterotrophy in orchids. However, the adaptive significance of fungal-derived carbon in mixotrophic plants remains largely unexplored. In this study, we investigated the photosynthetic orchid Oreorchis patens, a species related to the leafless genus Corallorhiza within the subtribe Calypsoinae. Using high-throughput DNA sequencing,