Pick up a mushroom from the forest floor and you are holding the tip of something almost incomprehensibly large. What you can see — the cap, the stem, the gills — is the smallest part of the organism.

Beneath your feet, threading through every gram of soil in every direction, is a network that has been growing, communicating, and keeping ecosystems alive for hundreds of millions of years.

Fungi are not plants. They are not animals. They are something else entirely — and the more scientists study them, the stranger and more remarkable they turn out to be.

Fungi Predate the Dinosaurs by an Enormous Margin

The earliest fungal fossils date back approximately 1.3 billion years — long before plants colonised land, long before animals crawled out of the sea, and vastly longer before the first dinosaur appeared around 230 million years ago. Fungi were among the first complex organisms to establish themselves on dry land, and it is now widely accepted that they made plant life on land possible in the first place.

The relationship between early plants and fungi — a symbiotic exchange in which fungi provided minerals and water to plant roots in exchange for sugars — allowed the first terrestrial plants to survive in nutrient-poor soils. Without that partnership, the greening of the land may never have happened. Almost every plant alive today still maintains a version of this ancient arrangement.

The Largest Living Organism on Earth Is a Fungus

In the Malheur National Forest in Oregon, USA, a single specimen of Armillaria ostoyae — the honey fungus — covers an area of approximately 9.6 square kilometres. It is estimated to be between 2,000 and 8,000 years old and is widely considered the largest known living organism on the planet by area.

What appears above ground as clusters of ordinary-looking mushrooms is in fact a single connected individual, its mycelium threading continuously through the soil across the entire area. The mushrooms are simply the reproductive structures — the equivalent of flowers on a plant. The organism itself is almost entirely invisible and almost entirely underground.

The Wood Wide Web: How Forests Communicate

Beneath every healthy forest floor is a fungal network so extensive and so functionally complex that researchers have taken to calling it the Wood Wide Web. Mycorrhizal fungi connect the root systems of different trees — sometimes of entirely different species — into a shared network through which nutrients, water, and chemical signals pass in both directions.

Studies have shown that established trees transfer carbon through these networks to younger seedlings growing in shade — effectively subsidising the growth of the next generation. When a tree is stressed by drought, insect attack, or disease, chemical signals travel through the network to neighbouring trees, which respond by increasing their own defensive compounds before any visible attack has reached them.

The network does not behave randomly. It appears to prioritise — directing resources toward younger or more vulnerable plants in ways that benefit the health of the forest as a whole rather than any single organism within it.

Some Fungi Glow in the Dark

Bioluminescent fungi — species that emit a continuous, cold green light — number at least 100 known species worldwide, found across forests in Brazil, Japan, and various tropical regions. The light is produced through a chemical reaction involving a compound called luciferin and is completely continuous — unlike fireflies, these fungi glow steadily throughout the night.

The purpose of this bioluminescence is not fully understood. Current research suggests it may attract insects that then disperse the fungus's spores, but this remains an active area of study. What is certain is that walking through a forest at night where these species grow produces an experience that has been described consistently as otherworldly — the forest floor glowing faintly green with no external light source.

Fungi Can Break Down Almost Anything

Fungi are among the most powerful decomposers in nature. Certain species produce enzymes capable of breaking down lignin — the tough structural compound in wood that almost nothing else in nature can digest efficiently. Without wood-rotting fungi, dead trees would accumulate indefinitely, locking up nutrients that the rest of the ecosystem depends on.

More remarkably, research has identified fungal species capable of breaking down plastics, crude oil, and even some synthetic compounds previously considered completely resistant to biological degradation. Pestalotiopsis microspora, discovered in the Amazon rainforest, can survive on polyurethane plastic as its sole carbon source — including in oxygen-free conditions. The implications for environmental remediation are significant and still being explored.

Spores: The Ultimate Survival Mechanism

A single giant puffball mushroom (Calvatia gigantea) can produce up to 7 trillion spores in a single fruiting. Fungal spores are among the most resilient biological structures known — capable of surviving extreme cold, radiation, desiccation, and in some cases the vacuum of space. They have been recovered from the upper atmosphere at altitudes of over 160 kilometres and from cores drilled deep into Antarctic ice.

This extraordinary dispersal capacity means that fungi exist essentially everywhere on Earth where conditions can support any life at all — in deep ocean sediments, inside nuclear reactor cooling systems, and on the exterior surfaces of the International Space Station.

Fungi challenge the way most of us think about life — what an individual organism is, what intelligence means, what a forest actually consists of. The mushroom on the forest floor is not a simple thing you step around. It is the visible expression of a system so old, so widespread, and so deeply woven into the fabric of life on Earth that removing it would unravel ecosystems we depend on entirely. Perhaps the most useful thing fungi teach us is that the most important processes in nature are almost always the ones happening out of sight.