Understanding fungi (mushrooms & toadstools)

CONTENTS

Structure of mushrooms & toadstools

Mould (a eukaryotic) growing on a lemon © Ita McCobb

The mushrooms and toadstools that we see when we are out walking are in fact the “fruiting bodies” of a parent organism growing underground, on trees or in decaying matter.

While the structure and some of the habits of fungi may seem similar to that of plants, fungi are not plants but belong to a completely separate category (kingdom) called “eukaryotics”, which also includes microorganisms such as yeasts and moulds.

Eukaryotes are the only organisms that can have tissue composed of different cell types – they can be 
unicellular (single cell) or multi- cellular (made up of many cells).

A fungus is made up of a “mycelium” – a unique microscopic network of fine white laments (called “hyphae”), which constitute the vegetative part of the fungus and through which the fungus/mushroom or toadstool obtains its nutrition.

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Mushroom & toadstool nutrition

Artist’s bracket Ganoderma applanatum © Ita McCobb

The reason fungi generally come in various shades of brown is that they lack chlorophyll and so cannot photosynthesize – they get their nourishment directly from living or dead plants or even the remains of dead animals.

The way fungi absorb their nutrition is extremely complex. Put simply, fungi excrete enzymes externally from their microscopic network of fine white laments (their hyphae) into the surrounding environment. These enzymes then break down the surrounding organic matter and the resulting chemicals are then absorbed by the fungi as nutrition.

The key to certain fungi preferences for specific nutritional environments, particularly their relationship with trees and other plant forms, lies in symbiotic relationships with other organisms built up over many millennia. 

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Mushroom & toadstool reproduction

The mushrooms and toadstools (and other forms of fungi) that we see when we are out walking are in fact the “fruiting bodies” (reproductive organs) of a parent organism that is growing underground or on trees or in decaying surface matter.

These “fruiting bodies” develop into species-specific forms, which then produce and distribute their offspring, not in the form of seeds, but as microscopic spores.

To produce a fruiting body, two mycelia of the same species bond and, given the right balance of nutrition, humidity, temperature, available light and sufficient water, they will form a fruiting body.

The larger forms of fungi are divided into two specific reproductive groups:

  • Spore droppers called “Basidiomycetes” 

  • Spore shooters called “Ascomycetes

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Spore droppers Basidiomycetes

Slippery Jack Suillus luteus © Ita McCobb

This is the most commonly encountered group of fungi. They reproduce by spores formed in club-shaped cells (called basidia) on their gills or tubes. When mature the spores simply drop off and are then distributed by passing animals or, most frequently, by the wind either directly or indirectly. For example, if they drop onto dead leaves, when the wind rustles the leaves the spores are blown away. Typical examples are: Boletes Boletus edulis, Honey fungus Armillaria mellea and Shaggy parasols Macrolepiota rhacodes.

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Spore shooters Ascomycetes

White saddle Helvella crispa © Ita McCobb

This group forms spores in club- or flask-shaped cells (called “asci”). When mature the spores shoot out of the cells through their tips (called “ascus”) with a certain amount 
of force, which causes them to float on the air or land on, hopefully, a suitable growing site. Typical examples are: Morels Morchella esculenta, Black truffles Tuber melanosporum and cup fungi such as the White saddle Helvella crispa.

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How fungi create wind to disperse spores

Fly agaric © Jennifer Hope-Morley

For a long time it had been thought that mushrooms relied on air currents to spread their spores, but research has shown that they are able to disperse their spores over a wide area even when there is not a breath of wind – by creating their own!

“The conventional view is that fungi enjoy little control over the mechanism of dispersal,” said Prof Emilie Dressaire, Trinity College, Hartford, Connecticut. “A spore falling from the mushroom cap can only hope to be picked up by a favourable air flow and carried away from the gap between the mushroom cap and the ground.”

Previous study showed that cup-shaped fungi (such as morels) stir a breeze by simultaneously ejecting spores from thousands of cells. The resulting puffs of air carry the fungal seed much further than if it had been simply dropped.

Whereas, capped mushrooms such as Fly agaric, Oyster mushrooms and Shiitake mushrooms make their own wind to disperse their spores. These mushrooms release water vapour that cools the air around them, creating convection currents, which then generate miniature winds that lift their spores into the air.

Dressaire and a colleague Marcus Roper from UCLA were able to visualize the spread of spores with laser light and a high-speed camera.

Although the study used laser light to visualize the spread of spores, it is possible to see this in a natural setting. “If you go into the woods with a flashlight at night you can see the spores going out in great big clouds,” said Roper.

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References: The British Mycological Society; Guides for the Amateur Mycologist – No.4, Guide for the Kitchen Collector:Preservation and Cooking of Fungi, Shelley Evans, BMS, 1994; Identifying Mushrooms, Peninsula Mycological Circle; How to tell if a mushroom is friend or foe, Jo Kessel, Daily Telegraph, 26 Oct 2010; Champignons vénéneux, E. Garnweidner, Mini guide Nanthan tout terrain 1991; Oxford English Dictionary, Oxford University Press; Champignons, toxiques & comestibles, Institut Klorane; Collins Fungi Guide, Stefan Buczacki, Collins; Mushrooms, Roger Phillips, MacMillan.