Symbiotic associations between plants and fungi (mycorrhizae) began about 450 million years ago1. Most mycorrhizal associations are mutualistic, such that the host plant and mycorrhizal fungi exchange nutrients with each other2. However, mycoheterotrophs have evolved a special type of plant–fungi symbiosis in which a plant gets fixed carbon and other nutrients from fungal partners, rather than from photosynthesis3. One of the most interesting characteristics of orchids is the reliance on fungi for seed germination and nutrient absorption, for example, through formation of mycorrhiza with fungi. Over 99% of orchids show partial mycoheterotrophy in which young plants obtain carbon (C) nutrients from fungi prior to the development of green leaves, while adult plants are autotrophic. The extreme type of mycoheterotrophy in orchids is obligate mycoheterotrophy, in which plants are achlorophyllous (lack chlorophyll) throughout their life cycle and therefore fully dependent on fungi for nutrition.