For most of modern life, mushrooms have been filed away as an ingredient. An earthy note in a sauce. A garnish. A craving.
They are a separate kingdom of life. Older than forests, foundational to almost every terrestrial ecosystem, and, in evolutionary terms, closer to you than to any vegetable on your plate.
That last fact alone should rearrange your sense of the living world.
DefinitionsWhat Is a Fungus?
Fungi do not photosynthesise. They cannot make their own food, so they eat, and they do it by pushing digestive enzymes out into the world and absorbing what dissolves. A fungus turns itself inside out to have a meal.
The mushroom you can see is not the organism. It is the fruiting body, the reproductive structure, a temporary thing pushed up to release spores. The organism itself is the mycelium, a network of threads finer than hair, running through soil or wood, sometimes for hectares.
A mushroom is to a fungus roughly what an apple is to an apple tree.
TaxonomyYou Are Closer Kin to a Mushroom Than a Mushroom Is to a Plant
Fungi and animals share a common ancestor that neither shares with plants. Both belong to a group called the Opisthokonta, named for a single feature: the propulsive flagellum sits at the back of the cell, pushing rather than pulling. Your sperm swim that way. So do the spores of certain primitive fungi.
Fungi build their cell walls from chitin, the same material as an insect's shell. Plants use cellulose. Fungi store energy as glycogen, exactly as you do. Plants use starch.
On the tree of life, the branch leading to mushrooms and the branch leading to you separated after both had already parted company with the plants.
ScaleWe Have Named Perhaps a Twentieth of Them
Hawksworth and Lucking, reviewing the evidence in 2017, put the likely number of fungal species at between 2.2 and 3.8 million. Roughly 155,000 have been formally described. That leaves ninety-five percent of a kingdom unnamed.
Every handful of forest soil almost certainly contains species nobody has written down. We map distant galaxies with more confidence than we map the ground under a single tree.
Hawksworth DL, Lucking R. "Fungal Diversity Revisited: 2.2 to 3.8 Million Species." Microbiology Spectrum, 2017.
CordycepsThe Zombie Fungus Is Not the One in Your Coffee
You have probably met cordyceps through a video game, a television adaptation, or a nature documentary narrated in a hushed voice. It deserves a more careful introduction, because three different organisms are being confused.
Ophiocordyceps unilateralis: the one that takes over an ant
This is the zombie fungus. It infects carpenter ants in tropical forests, and in the final hours of the ant's life it drives the animal to leave its colony, climb, and lock its mandibles onto a leaf vein at a height where humidity and airflow favour the fungus. The ant dies there. A stalk grows out of its head and rains spores onto the trail below.
Extraordinary work by Hughes and colleagues has shown the fungus does not invade the ant's brain at all. It surrounds the muscle fibres and controls the body directly, leaving the brain intact and, one assumes, watching.
Cordyceps militaris: the one people actually take
A bright orange, club-shaped fungus, cultivated on a controlled substrate, containing cordycepin and adenosine. It infects moth pupae in the wild. It has never zombified anything with a nervous system worth the name, and it is the species in almost every cordyceps supplement sold anywhere.
Ophiocordyceps sinensis: the one worth more than gold
The Himalayan caterpillar fungus. In India it is Keeda Jadi, in Nepal Yarsagumba. It colonises a ghost moth larva underground and sends a single dark stalk into the light. It cannot be farmed, and a kilogram can cost more than a kilogram of gold.
No Cordyceps or Ophiocordyceps species can infect a human being. Not one. Our body temperature alone is far outside the range they can survive in, and there is no evolutionary path from an ant's nervous system to yours.
The fungus in the video game is fiction. The fungus in the jar is a mushroom.
MycorrhizaeThe Wood Wide Web, and Why Scientists Are Arguing About It
Here is the story you have heard. Beneath the forest, fungal threads connect tree to tree. Old "mother trees" send sugar to their seedlings through the network. Trees warn each other of insect attack. The forest is a single, cooperating superorganism.
Here is what is actually established.
- Mycorrhizal fungi are real and vital. Around ninety percent of land plants form partnerships with fungi at their roots, trading sugars from photosynthesis for water and minerals the fungus is better at extracting. This is settled science and it is roughly four hundred million years old.
- The fungal threads do link plants underground. Common mycorrhizal networks exist.
- What travels along them, how much, in what direction, and whether it benefits the receiving tree, is not settled at all.
In 2023, Karst, Jones and Hoeksema published a review in Nature Ecology and Evolution examining the evidence behind the popular claims. They found that the most-repeated conclusions rested on a small number of studies, that citations of those studies had drifted steadily away from what the studies actually reported, and that unsupported claims about mother trees and forest-wide communication had become established in the popular literature through repetition rather than evidence.
The wood wide web is a beautiful idea. It is also, in its strongest form, an idea that has outrun its data.
We include this because the fungal kingdom does not need to be exaggerated. What is verified is astonishing enough: a four-hundred-million-year-old partnership between two kingdoms, without which there would be no forests, and probably no land plants at all.
Karst J, Jones MD, Hoeksema JD. "Positive citation bias and overinterpreted results lead to misinformation on common mycorrhizal networks in forests." Nature Ecology & Evolution, 2023.
BioluminescenceFungi That Glow
Around eighty species of fungi produce their own light. Not reflected, not phosphorescent. Chemical light, made by an enzyme acting on a molecule called luciferin, the same principle a firefly uses and a completely separate evolutionary invention.
The fungal luciferin was identified in 2015 as a compound derived from hispidin, and the full pathway was described two years later. It is the only fully characterised bioluminescence system in the whole of the eukaryotes.
Why they glow was long a mystery. In 2015, Oliveira and colleagues showed that Neonothopanus gardneri, a Brazilian species, controls its glow on a circadian rhythm, brightening at night. They then put out fake glowing mushrooms made of acrylic resin, lit from within. The insects came. The glow attracts spore dispersers, and the fungus chooses its hour.
ScaleThe Largest Living Organism on Earth Is a Fungus
Not a whale. Not a redwood.
In the Malheur National Forest in Oregon there is a single individual of Armillaria ostoyae, the honey fungus, whose mycelium covers roughly 2,385 acres, about 965 hectares, or nearly ten square kilometres. Estimates of its age begin around 2,400 years and run as high as 8,650.
It is not a mushroom you can photograph. It is a continuous body of fungal tissue running through the soil and the roots of the trees it is slowly killing, genetically identical throughout, and it has been there since before the Buddha.
Life can be enormous without being visible. We simply were not looking down.
PhysicsThe Fastest Flight in Nature
Pilobolus, the hat-thrower, grows on herbivore dung and faces an awkward problem: no grazing animal will eat grass next to its own droppings. To complete its life cycle, the fungus must get its spores far enough away to land on clean grass.
It builds a pressurised, fluid-filled cell beneath the spore mass, aims it at the light, and fires. Yafetto and colleagues measured launch speeds of roughly 25 metres per second, about ninety kilometres per hour, with accelerations among the highest ever recorded in a living thing.
No muscles. No nervous system. Turgor pressure, a lens, and four hundred million years of practice.
Yafetto L, et al. "The fastest flights in nature: high-speed spore discharge mechanisms among fungi." PLoS ONE, 2008.
Hericium erinaceusLion's Mane, and What We Are Allowed to Say
It looks like a frozen waterfall. A white cushion hanging from hardwood, covered in soft spines one to four centimetres long. In Japan it is yamabushitake, the mountain-monk mushroom. In China, hou tou gu, monkey head. It has been eaten as food in both countries for centuries, and it is delicious, with a texture close to crab.
Almost every brand selling it makes a promise about what it does inside your skull. We are not going to. Under Indian law a health claim on a food must be substantiated, and the published human literature on this species is small, short, and would not carry it.
What we will say is chemistry. The fruiting body contains a compound family called hericenones. The mycelium contains a different family, the erinacines. They are not the same molecules and they do not live in the same part of the organism, which means any product advertising erinacines while claiming to be a fruiting-body extract is wrong about one of those two things.
Trametes versicolorTurkey Tail, the Recycler
It grows in overlapping fans on fallen wood, banded in browns, creams, greys and improbable blues, and it is one of the most widespread fungi on Earth. It is found on every continent except Antarctica.
Turkey Tail is a white-rot fungus, which is a genuinely remarkable thing to be. Wood is mostly cellulose bound in lignin, a molecule so structurally awkward that for tens of millions of years after trees evolved, almost nothing could break it down. Dead trees simply piled up. A large part of the world's coal is the residue of that inability.
Then fungi learned to digest lignin, and the carbon started moving again.
Turkey Tail turns endings into beginnings. Without white rot, a forest would eventually bury itself in its own dead.
TuberTruffles: The Underground Currency
A truffle is the fruiting body of a fungus that has decided not to bother with the air. It ripens entirely underground, bound to the roots of oak, hazel or beech, and it solves the spore-dispersal problem by smelling so overwhelming that an animal digs it up and eats it.
This is why truffles cannot simply be farmed the way a crop is farmed. Truffle orchards exist, and they work, but they take a decade to yield and the yield is never certain, because it depends on soil chemistry, rainfall, the health of the host tree, and whatever else is living in that patch of ground.
A truffle is not grown. It is negotiated, between a fungus, a tree, and time.
CodaThe Quiet Kingdom Beneath Everything
Fungi are not a trend, and they are not superfoods. They are a kingdom that predates forests, without which no forest could stand, and which recycles nearly every dead thing on land back into soil.
They express something that looks a great deal like intelligence, using no brain at all. They solve engineering problems with turgor pressure. They fed the first plants onto land, and they will digest the last of us.
We have named under five percent of them.
And this we can say with confidence: the fungal kingdom has been holding the world up from below for four hundred million years, working quietly, waiting for anybody to look down.
