Kingdom of Fungi

Courtesy: text fragments below are from the first chapter of the book: “From Another Kingdom, The Amazing World of Fungi”, published by the Royal Botanic Garden Edinburgh

“Fungi are a unique and extraordinary group of organisms. They play many important roles in our everyday lives and are essential for the functioning of live on our planet. Although fungi have been lumped together with plants in the past, they are only very distantly related to them. In fact, fungi are more closely related to animals, including humans, than they are to plants. Fungi are so distinct from plants and animals that they represent an entire kingdom of organisms in their own right, and a large and diverse kingdom at that.

It has been estimated that there are around 1.5 million species of fungi, but only about 100.000 have been named so far. Recent results based on variation at the molecular level (DNA and proteins in particular) suggest that even this large figure may turn out to be a gross underestimate of the number of fungal species. The huge number of different fungi is truly remarkable when you consider that worldwide there are only about 400.000 species of flowering plants and 90% of these have been named. Even though fungi are so numerous, their significance can be overlooked as they remain hidden. Knowing where to look and what to look for is the first step into the fascinating and beautiful – and at times bizarre – world of fungi. This book introduces their enormous diversity and their great importance in sustaining life on Earth. It focuses on the many ways in which fungi touch human lives, from cultural associations to their often unappreciated role in everyday life. From human perspective fungi can kill and cure us. It is not surprising that there are mixed perceptions of fungi.”

Dutch DNA Biotech focuses together with the Royal Botanic Garden Edingburg on the huge debt of gratitude we all owe to fungi.

Photo credit: bob in swamp / Foter / CC BY

“What makes a fungus?

When thinking of fungi, the first thing that comes to mind is mushrooms, toadstools and possibly bracket fungi. However, these structures are the large sex organs of only an extremely small proportion of species within the Kingdom Fungi as a whole, and they belong to what are often loosely termed ‘macrofungi’. These fungal sex organs are equivalent to the flowers/fruits of flowering plants. Even for the fungi that produce these sometimes beautiful and exotic structures, they are just ‘the tip of the iceberg’ of the whole fungus, its main body usually being largely hidden in whatever it is growing on. Unlike the ephemeral sex organs, known as fruit bodies, the hidden subterranean part of the fungus lives not just for a few days but for several months and often for many years.

So what actually makes a fungus and distinguishes it from a plant, animal or bacterium? It turns out there is not just one distinguishing feature, but rather a combination of attributes which make fungi distinctly unique organisms.

Photo credit: Derek Keats / Foter / CC BY

The first characteristic feature is that the main feeding body of most fungi either is made of microscopic, filamentous tubes called hyphae, collectively termed a mycelium, or the fungus exists as individual yeast cells. There are fungi that can switch between having hyphal or yeast growth forms.

The second characteristic is that nearly all fungi do not move. A feature they share with plants. Like plants, fungi achieve ’movement’ via growth, as is amply demonstrated by time-lapse photography. It is their rigid cell walls that prevent fungi form moving in the rapid responsive way animals can. Unlike plants in which cell walls consist largely of cellulose, most fungal cell walls contain chitin. Chitin is a tough compound, and is also found in the external skeletons of insects and other arthropods such as crustaceans.

The third characteristic of fungi is that unlike plants, they cannot manufacture food using simple compounds and energy from sunlight through photosynthesis. Instead, they obtain their energy from the breakdown and digestion of organic matter, a feature they share with animals. Fungi feed by absorbing soluble molecules derived from the wide variety of materials they grow on and in. Small molecules such as simple sugars can be absorbed directly, but larger molecules, such as plant cellulose, must first be broken into smaller ones. Fungi achieve this by secreting appropriate enzymes into their surrounding environment. Fungal feeding is therefore sometimes described as ‘external digestion’, which contrasts with the internal digestion of higher animals. Fungi secrete a vast range of enzymes and these allow digestion of the multitude of organic resources available  on planet Earth.

The fourth defining characteristic of fungi is that they produce a huge range of different types of spores and these are involved in asexual or sexual reproduction. Although some lower plant, such as algae, mosses and ferns, form spores, they do not produce the extraordinary array of different spore types with the multitude of functions that are characteristic of fungi.”

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