Underground Networks — The Wood Wide Web
How fungi wire forests together — and why scientists are still debating what it all means
1. What Is a Mycorrhizal Network?
Beneath every forest floor lies a hidden world. A mycorrhizal network (also called a common mycorrhizal network, or CMN) is a vast underground fungal web that physically connects the roots of multiple plants, potentially enabling them to share nutrients, water, and chemical signals.
The individual threads of the fungus are called hyphae (singular: hypha). Each hypha is only a few micrometres wide — far thinner than a human hair — yet collectively they can extend for kilometres through the soil, linking tree to tree, shrub to seedling.
Two Major Types of Mycorrhizae
Arbuscular Mycorrhizal (AM) Fungi
- Penetrate inside root cortical cells
- Form branching structures called arbuscules (nutrient-exchange interfaces)
- Associate with ~80% of land plant families (grasses, crops, many hardwoods)
- Phylum: Glomeromycota
Ectomycorrhizal (ECM) Fungi
- Thread between root cells without penetrating them (forming a Hartig net)
- Encase root tips in a visible fungal sheath (mantle)
- Associate with ~2% of plant species — but these include dominant forest trees (pines, oaks, birches, beeches)
- Phyla: Basidiomycota and Ascomycota
Mycorrhizal fungi colonise over 80% of all land plant roots, and this symbiosis has evolutionary origins stretching back over 400 million years — to the very first land plants in the Ordovician–Silurian period. It is one of the oldest and most widespread mutualisms on Earth.