What are Mushrooms?
The word “mushroom” is a loose term and covers any fungus with a visible spore-producing fruiting body.
Typically this has a fleshy stem, cap and gills but may also include the leathery brackets and other forms.
Here the term will be used for the common stalk, cap and gill fungi.
Other mushrooms include the puffballs and stinkhorns.
It includes some Ascomycetes but mostly Basidiomycetes.
Approximately 14,000 species of mushrooms have been described worldwide.
Basic structure of mushrooms.
Fungi are made up of very fine filamentous cells or hyphae which, when massed form a mycelium.
1. The underground vegetative mycelium is 90% of the bulk of the fungus and may last for years.
2. The visible reproductive mycelium – the mushroom – produces the spores.
This may be transient as in the Inkcaps which only last a day or last for years like some leathery brackets.
Fungi have no chlorophyll so cannot manufacture their own food.
Instead they secrete enzymes which break down organic matter which is then absorbed.
Unless interrupted the mycelium spreads outwards in all directions in search of more organic matter.
This pattern of growth is responsible for the Fairy Rings commonly seen on lawns.
It is also seen in lichens which are largely composed of fungi.
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The mushroom stem, stalk or stipe.
The stem may be long or short, thick or thin, solid or hollow.
It may be cylindrical or swollen at the top, centre or base.
It is often white but can be shades of orange, brown or yellow.
The surface may be smooth, grooved or ridged.
There may be coloured fibrils or a reticular network on part or all of it.
If there is a ring it may be single or double, rigid or drooping, wide or narrow and variously coloured.
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The mushroom veils.
1. The Universal veil.
The earliest macroscopically visible indication of a new fruiting body may be a small ovoid egg/
This egg or button has a protective membrane – the universal veil.
As the fruiting body grows the veil ruptures but remnants may remain.
Those at the base of the stem form the volva.
On the top of the cap they are scales, warts, powder or a central patch.
2. The Partial and marginal veils.
Some Basidiomycetes, especially the Agarics, have a second or partial veil.
This extends from the stem to the edge of the cap to protect the young gills.
When it ruptures it may leave remnants around the stem – the ring or annulus.
Tags around the cap edge are known as the marginal veil.
Some mushrooms have no veils, some have one or the other and some have both.
They sometimes disappear as the mushroom ages.
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Mushroom cap – contour of the edge.
There are numerous descriptive terms for variations in the contour of the cap edge.
- Plain – the junction of the upper and lower surfaces is a straight line.
- Incurved – upper edge turns down to a sharp point where it meets the gills.
- Rounded – the junction of the upper surface and the gills is a rounded curve.
- Upturned – the edge is only slightly turned up.
- Revolute – the edges of the cap rolls upwards.
- Involute – the cap turns down and the edge is rolled inwards.
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Gills.
Gills are the thin blade-like plates or ribs under the cap of some mushrooms.
They support the hymenium or spore bearing layer.
They usually radiate from a central point and are easily separated from the rest of the cap.
Initially all gilled mushrooms were in the order Agaricales.
It is now known that they have evolved in other orders but still in the class Agaricomycetes.
They are seen in some genera in the orders Boletales, Gloeophyllales, Polyporales and Russulales.
Some Cantharellales have false gills which must be distinguished from true gills.
In some poroid fungi the pores form gill-like structures that are difficult to seprate from the cap.
There is much variation in the gills of different mushrooms and, again more descriptive terms.
Features to look for include the position of the gills in relation to the stem (free, attached or running down it).
Whether they are thick or thin, close or remote, any branching, long or short and colour.
There are also many terms for the appearance of the junction of the cap and gills including:
- smooth – a straight line.
- fimbriate – a fine, fringe-like appearance.
- dentate – fine, regular teeth-like projections.
- serrate- larger, regular teeth.
- undulate – smooth edged waves.
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Spore production in the Basidiomycetes.
Basidiomycetes produce spores on club-shaped projections which grow from basidia cells.
The basidia cells line the hymenium which is on, or in, the fruiting body.
Commonly seen mushrooms have the hymenium on gills under the cap.
The bracket fungi have tubes lined with basidia and puff balls have internal hymenia.
Spore release may be either active (e.g. puffballs) or passive (wind, insects etc.).
Spore release lasts a few days in gilled mushrooms but up to years in some bracket fungi.
Spores are minute but produced in massive numbers.
Spore colours include white, black, brown, pink or purplish.
Reproduction can be by mitosis (asexual) or meiosis (sexual).
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Fungal associations.
Many fungi have important symbiotic relationships with organisms from other Kingdoms.
Over 90% of all plant species have a relationship with a fungus.
The fungus obtains carbohydrates the plant has made by photosynthesis.
The fungus greatly improves the absorption of water and minerals by the plant.
Lichens are a symbiotic relationship between fungi and algae or cyanobacteria.
Some ants cultivate fungi.
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Competition.
Organisms are always competing for food and space.
Fungi use various techniques to kill or inhibit competitors.
These include the production of antibiotics or secondary metabolites.
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Identification of mushrooms.
In identifying fungi the starting point is still the macroscopic appearance of the fruiting body.
There are a large number of descriptive terms used for this.
Various authors can use different terms and different groupings.
Within any group there are exceptions, variations and atypical features.
The genus of a specimen can often be determined but species identification is more difficult.
Points to note include:
- the substrate is it growing on and how it is attached to it,
- the shape of the fruiting body, size, colour, texture, and smell,
- are there remnants of the universal or marginal veils on the stem and cap,
- the type, and details of, the spore bearing layer,
- if there are gills, do they attach to the stem or run down it,
- the colour of any spores that may have fallen onto adjacent structures,
- other details such as the presence of any exudate, does it bruise when touched etc.
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Grouping of mushrooms.
Grouping is an arbitrary process of dividing a large number of things into groups.
It is not classifying which is a scientific process.
There are a number of macroscopic features by which fungi can be grouped.
Another feature is the appearance of the spore bearing layer or hymenium (gills, pores etc.)
1. Grouping by shape.
- Stipitate fungi are the typical “mushrooms” mostly with a round cap and central stalk.
- Bracket fungi form fan-shaped, tough fruit bodies usually with no stalk.
- Crust or corticioid fungi are flat like a paint splash but may form small caps.
- Then a variety of shapes — club, coral, stinkhorns, puffballs etc.
2. Grouping by the spore forming layer or hymenium.
- Gilled fruit bodies have the hymenium on vertical plates under the cap.
- Poroid fruit bodies have vertical tubes opening by pores – the Polypores.
- Other hymenia including teeth (hydnoid), smooth, wrinkled (merulioid), spines,
internal, or on the external surface.
Whichever way fruit bodies are grouped there is some overlap between the groups.
Species of the same genus can end up in different groups depending on peoples definitions.
Most ‘mushrooms’ have gills but some have false gills or pores.
Most brackets have regular pores but some have gills, teeth spines etc.
Crusts may be smooth, have pores, teeth etc.
Examples of grouping some common fungi by the hymenium (spore formiing layer) gives:
- Mushrooms with true gills e.g. Agaricaceae, Amanitaceae, Marasmiaceae, Pleurotaceae and some Polyporaceae.
- Mushrooms with false gills e.g. Cantharellaceae with Cantharellus & Craterellus.
- Mushrooms with pores e.g. Ganoderma, Piptoporus, Pycnoporus and Trametes.
- Mushrooms with internal spores includes Puffballs, Earthstars, Birds nest fungi and Cup fungi.
- Mushrooms with surface spores includes a number of very different types.
This includes Club & coral fungi, Crusts, Jelly fungi, Stikhorns and Tooth or spine fungi.
Whatever grouping is used it must help in identifying specimens.
J.F.
