Matthias C. Rillig, Anika Lehmann, Luisa Lanfranco, Tancredi Caruso, David Johnson

The current use of the term ‘common mycorrhizal network’ (CMN) stipulates a direct link between plants formed by the mycelium of a mycorrhizal fungus. This means that a specific case (involving hyphal continuity) is used to define a much broader phenomenon of hyphae interlinking among plant roots. We here offer a more inclusive definition of the common mycorrhizal network as a network formed by a fungus among plant roots, irrespective of the type of connection or interaction, not limited to direct hyphal linkages. We propose the term ‘common mycorrhizal networks with hyphal continuity’ (CMN-HC) to capture the more specific case, which is important to study for some (notable carbon and nutrient exchange), but not all functions of a common mycorrhizal network. In addition, we introduce the term ‘common fungal network (CFN)’ to include networks of any type of connection formed by any type of fungus; this includes also non-mycorrhizal fungi, and indeed a combination of non-mycorrhizal and mycorrhizal networks. We feel this new set of three hierarchical terms (CMN-HC, CMN and CFN) can usher in a period of research activity unburdened by some of the difficulties (logistics, experimental design challenges) of studying CMN-HC and thus can help attract additional researchers to this fascinating topic of mycorrhizal ecology.