1. What are fungi?
Fungi are uni- or multicellular eukaryotic organisms that are neither plants nor animals.
They have no chlorophyll so have to absorb all their nutrients and they reproduce by spores.
The term includes mushrooms, yeasts, rusts, smuts, puffballs, truffles, morels, and moulds.
Because moulds, yeasts, mushrooms, slime and water moulds superficially resemble each other they were originally included in the lower plants with mosses, liverworts and ferns.
In 1969 Fungi were recognised as a distinct group and it is now known that they are more closely related to animals than to plants.
One current scientific classification is:
Domain Eukaryota > Kingdom Fungi > Sub-kingdoms including Ascomycota and Basidiomycota.
The kingdom includes a huge diversity of shapes, habitats and life cycles.
It is estimated that there may be up to 5 million species with only about 5% formally classified.
They all require water and oxygen to survive.
Their cell walls are rigid and contain chitin rather than cellulose.
Growth is by budding or elongation of the hyphal tips.
Reproduction is by spores either asexually (by mitosis) or sexually (by meiosis).
Most live on the land but they can be found almost anywhere.
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 and/or cyanobacteria.
Some ants cultivate fungi.
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2. Structure of fungi.
Fungi are made up of very fine filamentous cells or hyphae which, when massed, form a mycelium.
1. The persistent vegetative mycelium penetrates the surface of the substrate and absorbs nutrients.
2. The transient reproductive mycelium produces the spores.
Most fungi are inconspicuous because of their small size but may become obvious when fruiting.
They exist in two main forms:
1. Unicellular fungi or yeasts.
Yeasts are single cells which multiply by budding off new daughter cells.
They are important in bread making and in brewing.
2. Filamentous fungi. There are two main forms:
Multicellular filamentous fungi – the moulds.
Macroscopic filamentous fungi – the mushrooms.
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3. Classification of fungi.
The Encyclopaedia of Life has over 60 different classifications for fungi that have been proposed over the years.
The two main groups in the Kingdom (ranked as Phyla or Divisions depending on the classification used) are the Ascomycota and the Basidiomycota and between them they contain the vast majority of known fungi.
The placement of fungi into one of these phyla depends on how their sexual spores are formed.
Reproduction in fungi can be asexual (the commonest method) or sexual (fusion of two nuclei).
a.) Ascomycetes or sac fungi.
Many are tiny but the larger ones include morels, a few mushrooms, truffles, yeasts, and powdery mildews.
They produce spores within microscopic cells called asci on the fruiting body.
- In cup fungi the asci line the surface of an open cup or disk.
- In flask fungi the asci are in a chamber with a narrow opening at the top.
b.) Basidiomycetes or club fungi.
These produce spores on club shaped projections which grow from basidia cells.
Best known in this group are mushrooms whose gills are lined with spore bearing basidia.
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4. Phylum Basidiomycota (club fungi).
The Basidiomycetes are characterised by having spores produced on microscopic club-shaped cells called basidia.
It is a large phylum of 31,515 species containing most of the commonly seen fungi.
Basidiomycetes are the filamentous fungi (yeasts are unicellular).
Basidiomycota comprise three subphyla, 19 classes, 52 orders, 177 families, 1,589 genera, and 31,515 species.
The 3 sections are the rusts, the smuts and the Agaricomycotina.
Agaricomycotina species, in around 153 families are the ‘mushrooms’.
It include the familiar Agarics, puffballs, stinkhorns, coral, jelly and other fungi.
They are made of hyphae in the form of a permanent mycelium and a transient fruiting body.
The spore producing basidia are on the gills or tubes or on the surface depending on the form of the fruiting body.
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5. Identifying and grouping mushrooms.
Grouping is an arbitrary process of dividing a large number of things into groups.
It is not classifying them which is a scientific process.
In identifying fungi the first thing to consider is their gross appearance.
A common one is by the fruit body they form (crust, bracket etc.).
Another 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 their shape and the type of hymenium.
This results in various species of the same genus ending 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.
In the Fungi section I have used the shape of the fruiting body, then the hymenium.
J.F.
