The Kingdom of Fungi

A Hidden Kingdom

After a rainy night, mushrooms can appear in a field or forest as if by magic, sprouting up where there were none the day before. But these mushrooms are not magic, and they are not plants. They are the visible sign of one of the strangest and most important groups of living things on Earth: the fungi.

For a long time, people thought fungi were a kind of plant. We now know they are so different that scientists give them a whole kingdom of their own, separate from plants and animals. Surprisingly, fungi are actually more closely related to animals than to plants.

Scientists who study fungi are called mycologists. In this book, we will pull back the curtain on this hidden kingdom — discovering what fungi really are, how they grow and feed, and why life on Earth would collapse without them.

Not a Plant at All

To understand fungi, we first need to see why they are not plants.

The big difference is how they get their food. A plant is a producer: using sunlight, water and air, it makes its own food through photosynthesis. Fungi cannot do this at all. They have no green leaves and no way to capture sunlight. Instead, fungi must get their food ready-made from other living or once-living things, much as animals do.

There are other differences too. Plant cells are wrapped in walls made of cellulose, but fungal cell walls are made of chitin — the same tough material found in the shells of insects and crabs. This is one clue that fungi are closer to the animal branch of life.

So fungi sit in their own special place: not plant, not animal, but a kingdom all of their own.

The Body of a Fungus

When you picture a fungus, you probably think of a mushroom. But the mushroom is only a small part of the whole organism — like an apple on a tree, it is just the fruit.

The real body of most fungi is hidden underground or inside wood. It is made of millions of tiny threads called hyphae. Together, these threads form a vast, branching web called the mycelium. A single mycelium can spread out for metres, and the largest known fungus in the world stretches across many kilometres of forest soil, making it one of the biggest living things on the planet.

The mushroom we see above ground is the fruiting body. Its only job is to make and spread new fungi. When conditions are right — usually warm and damp — the hidden mycelium pushes up a mushroom so it can release its spores into the air. So every mushroom is a sign that a much larger, secret organism lies beneath your feet.

Eating in a Very Strange Way

Fungi feed in a way unlike any plant or animal, and once you understand it, the rest of the fungal world starts to make sense.

We eat by putting food inside our bodies, where our stomachs digest it. Fungi do the opposite: they digest their food outside their bodies. The hyphae release special chemicals called enzymes into whatever they are growing on — a fallen log, a piece of fruit, the soil. These enzymes break the food down into simple substances. The fungus then absorbs these nutrients straight through the walls of its threads.

This explains why fungi can live almost anywhere there is something to digest. We can sort them into three main lifestyles. Decomposers, also called saprotrophs, feed on dead matter like leaves and wood. Parasites feed on living plants or animals, sometimes causing disease. And mutualists form helpful partnerships, which we will explore soon.

Spreading by Spores

Fungi do not grow from seeds like plants. Instead, they reproduce using spores — tiny specks, far too small to see one on its own, that act a little like seeds.

A single mushroom can release billions of spores. They are so light that they drift on the slightest breeze, travelling huge distances. If a spore lands somewhere with the right food, warmth and moisture, it sprouts a thread that grows into a new mycelium, and the cycle begins again.

Fungi have many clever ways of spreading their spores. Some, like the puffball, burst in a cloud of dust when a raindrop hits them. Others grow brightly coloured caps or give off strong smells to attract insects that carry spores away. A few even fling their spores into the air with surprising force. Producing so many spores means that even if almost all of them fail, a few will always find a good home.

Partners and Recyclers

Now we reach the reason fungi are so vital to life on Earth: their work as recyclers and partners.

As decomposers, fungi are nature's great clean-up crew. When a tree falls or an animal dies, fungi move in and break it down, returning its nutrients to the soil for new plants to use. Without fungi, dead leaves and wood would pile up endlessly, and the nutrients locked inside them would never be released. In a very real sense, fungi keep the whole forest recycling.

Even more amazing is the partnership called mycorrhiza. The mycelium of certain fungi wraps around and into the roots of plants and trees. The fungus collects water and minerals from a huge area of soil and passes them to the plant. In return, the plant shares some of the sugars it makes by photosynthesis. Almost all plants on Earth rely on these fungal partners. Some scientists call the underground web of fungi linking many trees together the "wood wide web," because it can carry nutrients and even warning signals between plants.

Fungi and People

Fungi are not just important in the wild — they have shaped human life for thousands of years.

Some fungi are food. The mushrooms in your dinner are fungi, and so is the mould that gives blue cheese its flavour. A tiny fungus called yeast is one of the most useful of all: it makes bread rise and is used to brew drinks, by feeding on sugar and giving off bubbles of gas.

Fungi have also saved millions of lives through medicine. The first antibiotic, penicillin, came from a mould — a fungus that kills harmful bacteria. Today, many medicines still come from fungi.

But we must also respect fungi. Some cause diseases in plants, animals and people, and some wild mushrooms are deadly poisonous, looking almost identical to safe ones. That is why you should never eat a wild mushroom unless an expert has checked it.

What We Learned

We have explored a kingdom that is all around us yet easy to miss.

We learned that fungi are not plants but a kingdom of their own, unable to make food from sunlight and built from chitin like animals. The mushroom we see is only the fruiting body of a vast hidden network called the mycelium, made of threads called hyphae. Fungi feed by digesting food outside their bodies and spread by releasing countless spores. As decomposers and as partners to plant roots, fungi recycle the dead and feed the living, and they give people food, drink and life-saving medicine.

So the next time a mushroom appears overnight, remember the enormous, silent world working beneath it. The kingdom of fungi may be hidden, but life on Earth depends on it.

Want to keep exploring the unseen living world? Meet other tiny lifeforms in The Tiny World of Microbes, or discover how forests work in The Secret Life of Trees.