Fungi are one of the most diverse and fascinating branches of the tree of life. They are so different from other organisms that they are in a kingdom on their own. In recent years, more has been discovered about these incredible organisms, and we are starting to understand their importance. But, like so much of nature, fungi are under threat. So, it is now more important than ever to understand them. So, what are fungi? And why are they so important?

what are fungi
What are fungi?

What Are Fungi?

Fungi are a diverse group of eukaryotic organisms that include yeasts, moulds, mushrooms, and subterranean mycorrhizal fungi. They’re found across the globe in a wide range of different environments, including forests, the soil,  inside the human body, deep-sea hydrothermal vents, the Sahara Desert, and even Antarctica.

Some fungi are tough to classify into species as they can join together with other species and swap genes through a process called horizontal gene transfer. This means that they can adapt very quickly to new challenges and environments. Because of this ability, they can colonise many parts of the world and are incredibly successful. They can adapt to their surroundings very quickly, acquiring the necessary tools to overcome almost any obstacle. This makes them a powerful ally, as we will see later.

Unlike plants, fungi cannot photosynthesise, so they get their energy from breaking down and absorbing organic matter. Mycorrhizal fungi form mutualistic relationships with plants, whereby the plants feed the fungi, and the fungi help source nutrients for the plants and provide protection for their roots. Other fungi are pathogens, feeding off live plants, weakening, and even killing them. Fungi play a vital role in ecosystem function, helping to cycle nutrients and decompose organic matter.

What Are Fungi? Are They Plant or Bacteria?

A common question about fungi is whether they are plants or bacteria. This confusion comes from the fact that fungi only got reclassified in 1969. Before this, they were classified as plants. Now, they instead exist in a kingdom of their own. There are six kingdoms of life, as follows;

  • Plants
  • Animals
  • Archaebacteria
  • Protists
  • Eubacteria
  • Fungi

Fungi are in a kingdom of their own, meaning that they are not related to plants or bacteria. 

Why are Fungi so Important?

Fungi are important for various reasons, past, present and future. The entire terrestrial world would not be able to function without fungi. Let’s look at some of the reasons why fungi are so important to help us understand what fungi are. 


Fungi are primary decomposers, meaning they break down organic matter, cycling nutrients back into the ecosystem. Without fungi, there would be no soil, and the world might buried under dead wood! Fungi possess a wide range of enzymes that they use to start the decomposition process. They are key to breaking down the complex molecule, lignin that gives trees their strong, woody structure. 

As fungi are incredibly adaptable, they are great tools for bioremediation. This is the breakdown of environmental pollutants using deliberately introduced microorganisms. Fungi can break down petroleum, metals, dyes, pharmaceuticals, hydrocarbons, bleach and even pesticides (source). Oyster mushrooms are commonly used to clear up oil spills. It is believed that fungi’s potential for bioremediation – or mycoremediation as it is known – is only beginning to be understood. 


Fungi are a common source of protein for many animals, including humans. They are relatively easy to cultivate, and some are considered a delicacy in many cultures. With a recent push to reduce our society’s meat consumption due to environmental concerns, fungi often act as a substitute. Products such as Quorn are made from fungi. They are high in protein and very low in saturated fat, making them a healthy alternative to meat. 

Associations with Plants

Almost all terrestrial plants have a symbiotic relationship with mycorrhizal fungi. It is hypothesised that plants would not have been able to come out of the ocean millions of years ago without help from their fungal allies. 

Fungi help plants source nutrients and water from the soil, protect their roots from pathogens and pests, and help manage soil structure. Fungi also connect trees with other trees in an underground network. This is sometimes known as the wood-wide-web. Trees can transfer nutrients and sugars to one another through this network, helping to nurse young and ailing trees. They can also send chemical messages warning one another about potential pests and pathogens. 


Some fungi produce bioactive compounds that are used in medicine. Penicillin is a well-known example of a medicine made from the penicillin fungus. With the staggering diversity of fungal life only beginning to come to light, it is likely that many more medicines will be made from fungi in the future. 


Fungi – specifically yeast – have been used in fermentation for centuries. They are an essential element in the production of bread, beer, wine and other fermented products. 

Biological Control

A possibly contentious issue, biological control, is the introduction of a species to control the population of another. Fungi can be an important tool for biological control. For example, the rust fungus is useful in the control of Himalayan balsam, one of the UK’s most invasive plant species. A fungus called Beauveria bassiana is an effective control of aphids, adhering to their exoskeleton and slowly dissolving them.

Problems with Fungi

Many people still believe that fungi are a problem that should be eradicated, and in some cases, fungi can cause trouble. Mould causes problems for buildings in humid environments and for our food. Honey fungus is parasitic and kills trees. 

Several highly poisonous mushrooms are responsible for a number of deaths every year. Some examples are the flamboyantly named Destroying Angel and the fairy-tale Fly Agaric with its red cap and white spots.  The chemical compounds produced in some mushrooms can cause severe gastrointestinal distress when consumed. However, mushrooms cannot kill you unless you eat them, and they usually require pretty high doses. There is an air of fear surrounding eating wild mushrooms. This is because they are easy to misidentify, and the consequences can be dramatic. So many people try to avoid them.

What Would Happen if There Were No Fungi?

Fungi are important in agriculture, medicine, ecosystem function, conservation and more. 

Without fungi, there would likely be no other life on Earth. Plants support other kingdoms of life by providing carbohydrates and sugars from photosynthesis. But fungi also play an essential role in supporting other life forms and ecosystems. 

Importantly, wood only breaks down with the assistance of fungi. They possess the necessary digestive compounds to break down the strong natural structures in wood. Once fungi have started the process, other decomposers, such as bacteria and arthropods can start to process the wood. This returns carbon and nutrients to the soil. 

How Can I Learn More About Fungi?

Fungi are fascinating. In this article, we have only just scratched the surface of their incredible lives and answered the question of what are fungi. If you want to know more about these important and mysterious organisms, why not try our Fascinating Fungi course? It is comprehensive and captivating and will give you a good knowledge of fungi so you can understand why fungi are so important.