A beginner's guide to fungi: Nature’s hidden kingdom

Fungi are probably one of the world’s most unique and fascinating organisms. They are completely separate from plants and animals, and encompass mushrooms, yeast, mold, lichens, and rust (an organic fungus not to be confused with iron rust). Fungi are found everywhere on the planet; from our forest floors and trees, all the way to the bottom of the ocean, and even living inside our bodies. 

Up until 1969, fungi were falsely classified as plants, which meant that despite its importance and ecological value, it’s only recently getting the research and attention that they deserve. So if it’s not a plant, and it’s not an animal, what is it? And, what makes this spectacular organism so important for all life on Earth?

What exactly is fungi?

Fungi are what’s known as eukaryotic* organisms, meaning their cells contain a nucleus — just like all plants and animals. However, they differ in a few key ways. Firstly, fungi are heterotrophic, which means they get their nutrients by digesting organic matter, unlike plants which photosynthesise sunlight to grow. Their cellular makeup is also different; fungi have cell walls made of chitin, which is a tough and durable polysaccharide* that provides structural support and protection. Chitin also makes up the exoskeletons of many insects and crustaceans. 

Fungi reproduce both sexually and asexually, depending on the species and environmental conditions. Most fungi release tiny, airborne spores which grow into new fungi. Others break off filaments which grow into new individuals (called fragmentation). These produce genetically identical clones or the original organism. Sexual reproduction happens under stressful conditions like drought or lack of food, often between two different but compatible fungal types. This creates genetic diversity, which helps the fungi adapt to changing environments. 

Types of fungi

Fungi belong to their own kingdom — the Kingdom Fungi — which means it’s difficult to talk about them as just one thing, but the most common types of fungi you’ll see in your daily lives are mushrooms, molds, and yeasts.

Mushrooms

Mushrooms are the fruiting bodies of certain fungi, and are one of the most easily recognizable forms. There are approximately 14,000 different species of mushroom, but only 2,200 are edible, and even less that are widely studied and cultivated. While the iconic forest mushrooms are just the “flowers,” beneath the surface lies the mycelium, a vast network of thread-like structures called hyphae which make up the majority of the organism. 

The mycelium network is crucial to ecosystems as it breaks down organic matter, returning nutrients to the soil. This is the basis of the fungi’s symbiotic relationship with plants. The world’s largest known single organism is a fungal mycelium called Armillaria solidipes (honey fungus) in the Malheur National Forest in Oregon, which covers over 3.4 square miles. It’s been named the Humungous Fungus.

Mold

Not to be confused with mycelium, which are much more organized, molds are filamentous* fungi that can grow on lots of different surfaces. Mold is often very misunderstood, but includes a wide and diverse group of organisms. Molds play a major role in decomposition, which is why you’ll see it on food that has gone bad or is thriving in moist, warm, and nutrient-rich environments. 

Yet despite its initial purpose, mold has provided us with some incredible medical advancements. In 1881, bacteriologist Alexander Flemming accidentally discovered penicillin, a mold that could kill pathogenic bacteria, but didn’t attack white blood cells or human tissue. His discovery is one of the most important medical advancements of the 20th century. 

Yeast

Used in baking, brewing, and biotech, yeast is one of the most widely used and researched fungi. For thousands of years, humans have been using yeast to bake bread, ferment wine, and brew beer. This is because yeast causes fermentation as it feeds on sugars, producing alcohol (ethanol) and carbon dioxide in the process. Genetically engineered yeasts have also been made into bioethanol for clean energy, and it’s used in medicine to create insulin and other biopharmaceuticals.

Lichens

Lichens, another type of fungi often found on rocks, trees, soil, and even man-made structures like buildings and tombstones, are pioneer species with the ability to survive in extreme environments. Pioneer species are the first organisms to colonize an area, especially some kind of dramatic or disruptive disturbance like a volcanic eruption or wildfire, or in a previously barren environment. Lichens are also considered an indicator species because of their sensitivity to air pollution, which means that they’re the first organisms to be affected when pollution is high, indicating to scientists that something is wrong.

Role of fungi in nature

In nature, fungi have one main role: decomposition. Their job is so important that ecosystems would collapse without them, yet most of the time they are totally invisible. Their job is to break down organic matter, like dead plants and wood, as well as dead animals and animal waste. They break down the tough materials that bacteria can’t, and in doing so release carbon, nitrogen, and other nutrients back into the soil and air. This continuous cycle of decomposition is what makes fungi such an important part of the nutrient cycle, which is essential for plant growth and new life.

Around 90% of plants form symbiotic relationships with mycorrhizal* fungi. Fungi, like mycelium, will colonize plant roots, helping them to extend their reach into the soil and providing the plant with nutrients and minerals. The relationship between fungi and plants boosts growth and soil stability, and most importantly, helps entire forest ecosystems communicate and share resources — which is often called the Wood Wide Web. 

Why do we need to protect fungi?

Earlier this year, the International Union for Conservation of Nature (IUCN) assessed 1,300 fungal species and found 411 of them to be threatened with extinction. Deforestation, farming and climate-fuelled fires are driving increasing threats to fungi, and this number is just a small fraction of the 150,000 fungal species recorded to date — it’s impossible to know how many species have already been lost. 

Without fungi, there would be no way to decompose plants and other organic matter properly, meaning that the earth and soil would choke on the pile of dead things. Crop pests, invasive plants, and pathogens would spread more easily and natural population control would be lost. Nutrient cycling would be a thing of the past, and ecosystems would run out of usable nutrients over time.

Fungi’s role in nature cannot be understated, and yet despite its importance, it’s pretty misunderstood, and often ignored when we talk about how best to protect the planet. However, the Fungi Foundation is working to change that, and Planet Wild joined them in Chile to learn more about how and why fungi need to be part of the conversation when it comes to biodiversity protection.

By treating fungi with the same enthusiasm as plant and animal species, we can ensure that this unique species doesn’t continue to be forgotten. If enough countries back the Fungal Conservation Pledge and push the UN to include fungi in its global nature protection agreements, it could unlock a new approach to nature protection and protect entire ecosystems for good. 

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Glossary of terms

Eukaryotic: Organisms whose cells contain a nucleus and other membrane-bound organelles.

Polysaccharide: A large carbohydrate made of many sugar molecules (monosaccharides) linked together.

Filamentous: Describes something composed of or resembling filaments, which are thread-like structures.

Mycorrhizal: A symbiotic relationship between fungi and plant roots. This partnership is also known as mycorrhiza.