Mycoheterotrophic plants (MHP) lack chlorophyll and mostly have reduced shoots, leaves and roots, sometimes hardly resempling a plant at all. They tend to grow on the floor of deeply shaded tropical rain forests and it is no surprise that they are mostly found by mycologists. Assimilation of carbohydrates via photosynthesis is impossible and wouldn't  make much sense either in these habitats, hence, another source of carbon is necessary. MHP have long been misinterpreted as parasitic flowering plants, actively penetrating neighbouring plants with haustoria in order to participate from their host's assimilates. They have also been considered as 'saprophytes', but the breakdown of dead organic material is (as far as we know) impossible for plants. The truth is: they are cheaters! They cheat their mycorrhizal fungus in taking nutrients and carbon, whereas usually the plant gives assimilates to the fungus. We do not know yet if there is any advantage for the fungus at all, but I fear there is no. However, the little loss of carbon through a small plantlet shouldn't hurt much a fungus that probably is established in numerous other green plants.