Do

chlorophyllous orchids h que Bag Spotlightsaprotrophs [4]. Second, these orchids display much higher 13C abundance than the C3 plants that surround them. The achlorophyllous orchids that obtain their entire C from their mycorrhizal fungi (mycoheterotrophic orchids) have a 13C abundance identical to that of the saprotrophic or ectomy-corrhizal fungi that feed them (Figure 1), which are them-selves 13C-enriched compared with autotrophic plants [3,4]. Moreover, the green orchids that are partially heterotrophic (mixotrophic orchids) have a 13C content fungal source without fractionation. We speculate that the second explanation is likely, because an overlooked ecologi-cal niche of rhizoctonias indeed predicts 13C abundance close to that of autotrophic plants. Rhizoctonias revisited There is evidence that rhizoctonias do not exclusively depend on orchid mycorrhizae for their C nutrition, but have their own, independent nutritional niche. Their saprotrophy is only indirectly suggested by the observation of in vitro growth on dead and sometimes complex organic matter [1], but there is no direct evidence under natural conditions. Strikingly, the 13C abundance observed in ger-minating seedlings [5] does not fit the high 13C abundance expected for saprotrophic fungi (Figure 1) [4]. What then is the real ecological niche of rhizoctonias