Most of the fungi you will encounter in a forest are not what you see. The mushrooms above ground are the reproductive structures of organisms that exist primarily as networks of fine threads spreading through soil and through the roots of plants. These networks, collectively called mycorrhizae, form one of the most important ecological partnerships on Earth, and they were doing their work for hundreds of millions of years before anyone thought to name them.
The popular narrative around mycorrhizal networks has expanded rapidly in recent years, sometimes outpacing what the underlying research actually supports. This article explains what these networks are, what they demonstrably do, and where the more dramatic claims need to be qualified. The real story is more interesting than the simplified one, which is usually how it goes with biology.
What a mycorrhiza actually is
A mycorrhiza is a symbiotic association between a fungus and a plant root. The word literally means fungus root, and the relationship is intimate enough that in many species you cannot easily tell where the plant ends and the fungus begins. Two main types are most studied. Arbuscular mycorrhizae form inside plant root cells, growing branching structures called arbuscules where exchange happens, and they occur in roughly 70 percent of plant species, including most agricultural crops and grasses. Ectomycorrhizae form sheaths around the outside of roots and grow between the root cells without entering them, occurring in many tree species, including pines, oaks, beeches, and birches.
In both cases the underlying transaction is similar. The fungus receives sugars produced by the plant through photosynthesis, and the plant receives mineral nutrients, particularly phosphorus and nitrogen, that the fungus is far better at extracting from the soil than the plant's own roots are. It is a trade, carbon for minerals, carried out at the cellular interface where the two organisms meet.
Why plants need this partnership
Plant roots are limited in their reach. They can grow only where the root tip is, and they extract nutrients from the soil immediately around them. The hyphae of a fungal network are far thinner than the finest plant roots and can extend through hundreds or thousands of times the volume of soil that a root system alone could access. The fungus is, in effect, a vast outsourced extension of the root, reaching where the plant cannot.
This matters most for nutrients that are scarce, immobile, or chemically locked up in the soil. Phosphorus is the textbook example. In many soils phosphorus is present but bound to minerals in a form plant roots cannot use directly, and mycorrhizal fungi produce enzymes that liberate it and transport it through their hyphae to the plant. The relationship is ancient. Fossil evidence suggests mycorrhizal partnerships existed by the time plants first colonized land, roughly 460 million years ago, and the early colonization of land by plants may have been impossible without fungal partners providing access to soil nutrients. The green world above ground may owe its existence to a partnership struck underground.
The "wood wide web", and its caveats
In recent years, popular accounts have emphasized the idea that fungi connect different plants into communicating networks, the so-called wood wide web. Trees share carbon. Mother trees feed their offspring. Forests behave as collaborative super-organisms. The underlying science is more interesting, and more complicated, than that framing suggests. Common mycorrhizal networks, where the same fungal individual connects multiple plants, do exist, and there is good evidence that nutrients can move through them between plants. Whether that movement is meaningful at ecological scale, whether it is directional in the way some accounts suggest, and whether plants exercise any control over the process all remain active areas of investigation.
A 2023 review in Nature Ecology and Evolution examined the evidence for the most widely cited claims about common mycorrhizal networks and found the support thinner than the popular accounts implied. The basic phenomenon, that fungal networks can connect plants, is well established. The interpretation of that phenomenon as deliberate cooperation between trees is much less so. The gap between those two statements is where most of the popular storytelling lives.
Pull quote: Fungal networks really do connect plants underground. Whether trees use those connections to deliberately feed their kin is a much bigger claim, and the evidence for it is thinner than the headlines suggest.
What the research actually supports
Several findings are well supported and important. Mycorrhizal fungi substantially improve plant access to phosphorus, nitrogen, and water, an effect that is large and consistent across studies and species. Mycorrhizae influence plant community composition, since plant species that associate with similar fungi tend to grow together, while those that associate with very different fungi may experience competitive disadvantages near each other. And the fungal community itself is shaped by the plants present, since different host plants support different fungal communities, and management practices that disrupt those communities, heavy tillage, fungicide use, monoculture cropping, can have lasting effects on soil fertility.
What remains less certain is the degree to which mycorrhizal networks function as integrated communication systems. Carbon does move through them between plants under some conditions, but whether plants use them strategically to support kin or to signal stress is an open question that current data cannot definitively answer. It is also worth being clear about what "connection" means here, because the word does a lot of quiet work in the popular story. Two plants sharing a fungal partner are connected in the sense that a path exists between them, the way two houses on the same water main are connected. That is not the same as the plants choosing to send resources to each other, and conflating the two is where much of the overreach begins. The cautious version of the story is not a hedge. It is simply where the evidence currently sits, and the difference between a passive conduit and a deliberate signal is exactly the kind of distinction careful ecology has to insist on.
Implications for forestry and agriculture
The practical implications are substantial. In agriculture, maintaining healthy mycorrhizal communities is increasingly recognized as important for soil health and reduced fertilizer dependence. In forestry, restoration projects that ignore the fungal partners of native trees often fail, and replanted forests on disturbed soils may need fungal inoculation to thrive. The fungus is not an optional extra in these systems. It is part of the infrastructure.
For psilocybin mushrooms specifically, the relationship to mycorrhizae is mostly indirect, and worth clarifying because it is easy to assume otherwise. Most psychoactive Psilocybe species are saprotrophic, feeding on dead organic matter rather than partnering with living plants, as we discuss in our profiles of the psilocybin-producing genera. They participate in the broader fungal community of forests and grasslands without forming the kind of symbiotic partnerships that mycorrhizal species do. The famous green-and-gold image of fungi feeding trees is a different branch of the family from the one that produces psilocybin.
Why the detail matters
The story of fungi as the social network of the forest is genuinely compelling and partly true. But the version that gets repeated in popular media often glosses over what the science actually shows and overstates how well understood the dynamics are. Mycorrhizal networks are real. They are biologically and ecologically important. They probably do more than we currently understand. And they almost certainly do less than the most enthusiastic accounts claim.
The honest position, that this is an active and rapidly evolving area of research where careful claims need to be distinguished from speculative ones, is also the most useful one for understanding what fungi actually do in ecosystems. It asks a little more patience than the super-organism story, but it has the advantage of being true to the evidence, and the underground world it describes is remarkable enough without the embellishment.