Recently, many green plants forming Paris-type arbuscular mycorrhiza (AM) have been suggested to receive fungal carbon (Giesemann et al. 2020b, 2021). Whereas the enrichment of natural abundance of heavy stable isotopes (particularly ¹³C) has been considered as strong evidence for this ‘partial mycoheterotrophy,’ we show our own data on isotopic abundances and mycorrhizal colonization in Japanese plants and argue that the ¹³C-enrichment may not always be the result of acquiring carbon from AM fungi.