Chapter 1: THE WORLD OF FUNGI
In 1753 Carl von Linnaeus classified living organisms into two kingdoms: animal and plant, based
only on a macroscopic vision of the biosphere. Within the plant kingdom, he established a
subdivision: phanerogams and cryptogams. He included fungi into the class cryptogamia.
Nowadays, based on the constitution of organisms and on the mode of nutrition, the division of
living beings has been extended to five kingdoms (MARGULIS, 1985): Monera, Protista, Fungi,
Plant and Animal.
Absorption
Photosynthesis
Ingestion
The first three groups:
The Kingdom Monera includes prokaryotic organisms, which lack a membranebounded nucleus, chromosomes, and mitochondria and also do not carry out sexual
reproduction. Blue algae and bacteria are representatives of this Kingdom.
The Kingdom Protozoa includes eukaryotic organisms (cells with an independent
nucleus), and is defined by exclusion: they are not fungal, neither plant, nor animal.
Included in this kingdom are algae that are related to the plant world, protozoans related
to the animal world and myxomycetes to the fungal world.
The Kingdom Fungi includes eukaryotic organisms, which are equipped with flagella,
reproduce by spores and have a heterotrophic mode of nutrition by absorption; they lack
chlorophyll or other photosynthetic pigments, and have a cell wall composed of cellulose
and/or chitin. Their heterotrophic character (they are not able to synthesize organic
components) separates them from plant organisms and the presence of spores from
animal organisms.
1.1. General characteristics of fungi.
All macromycetes or fungi possess two
distinctive parts:
a. The mycelium. It is formed by a
series of threads or hyphae, in general
white-coloured, and grows out in the
ground predominantly in the humus
layer or surrounding roots, on leaf litter,
decaying wood and even on other
fungi, plants or animals. It constitutes
the vegetative part of the fungus. The
threads or hyphae grow out radially
and indefinitely in any direction. In
certain cases they form complete
circles referred to as “witch or fairy
rings” due to their spontaneous and
mysterious fructification.
b. The carpophore, commonly called
mushroom.
The
“mushroom”,
“carpophore”
or
“fruiting
body”,
constitutes the aerial part of the fungus.
Only a small part of the mushroom or carpophore is fertile, the zone known as “hymenium” is
either composed of gills, tubes, spines, and, in certain cases it has a smooth or slightly ribbed
surface.
The spores are produced in the hymenium and enable the spreading of a species. Once the
mature spore is released it may happen to land on an adequate substrate or not. In the majority of
the cases, spores do not encounter adequate conditions and are then lost. If the spore does
happen to land on an adequate substrate, it germinates and produces a very thin thread (primary
thread). When this thread or hypha meets up with another compatible primary hypha (produced by
another spore), they fuse and form a new hypha (secondary thread); the name applied to the
network of new threads or hyphae resulting from the fusion is mycelium.
Carpophore development
Finally, the fruiting body or mushroom that we observe above ground or that, in certain cases, lies
hidden in the soil substrate (e.g. truffles) is an extension of the mycelium or vegetative part of the
fungus. One single carpophore produces tens of thousands of spores and, in certain cases, up to
billions of spores (for example Langermannia gigantea). Every time that mature spores are
released and happen to land on an adequate substrate, a new cycle begins.
1.2. Macroscopic examination.
On carpophores or fruiting bodies, many details, which look insignificant at first sight, are of great
importance for them to be identified and classified.
a).- Cap.
The most common mushroom shape known is the umbrella shape though it can have many
different variations depending on the species. As a consequence, caps can be of various shapes
and colours: rounded, plane, concave, convex, mammilate, funnel-shaped, hemispheric,
campanulate...
The cuticle: it is the outer membranous layer covering the cap. In the identification process, this
surface feature is of great importance; attention should be given to its structure, texture and its
colour.
The appearance of the cuticle varies widely among species. It can be: viscid or dry; difficult or
easily separated from the underlying flesh; smooth or scaly, fibrillose, warty, tessellated or netted,
fragmented, wrinkled or cracked, etc.
The margin: the margin of the cap can be smooth, undulated, striate, grooved, scalloped, thin or
thick, etc.
SURFACE OF THE CAP
Smooth
Scaly
Tomentose
Fibrillose
Warty
Wrinkled reticulate
View from above
Villose
Zoned
Shaggy
1. Scaly
2. Squamulose
appressed
3. Squamulose
uplifted
4. Shaggy
5. Fibrillose
6. Wrinkled
reticulate
7. Rimose
8. Cracked
rivulose
9. Aerolate
cracked
10. Granular
b).- Hymenium.
This is the fertile part of the carpophore were the spores are located.
The shape of the carpophore usually reflects the situation of the hymenium. There are three main
categories as astart towards classification: whether the hymenium is internal, external or sited
beneath a cap.
- The gills: vertical thin walls situated at the underside of the cap growing from the cap margin
towards the stipe. Gills can be: separated e.g. distant from the stipe; free e.g. close to the stipe but
without touching it, adnate or adherent e.g. touching the stipe on a small contact surface and
decurrent e.g. running down a part of the stipe.
- Pores: small apical orifices at the end of tubes. For carpophores of the Boletales order and the
Polyporaceae family, the pores are situated in the inferior part of the cap (external hymenium
beneath a cap). The tubes can be of different colours, more or less short and difficult to separate
from the flesh. The pores can be round, elongated, single, double, angular… and they can be
attached to the stipe like gills e.g. they can be decurrent, adherent, free or separated.
- Spines: little prickles or spines pointing downwards from the hymenial surface (e.g. in the
Hydnaceae family). They can be short or long, large or thin, firm or gelatinous.
c).- Stipe.
The stipe, sustaining the cap, is an important macroscopic character in the determination of
species. Its colour, size, form, texture (fibrous or grainy), structure (hollow or solid) varies widely
between different species.
- Structure and shape: solid or hollow, thin or thick, bended, winding, tapered, flared, clavate,
bulbous.
- Flesh: fibrous, cartilaginous or grainy.
- The surface can be: reticulate, smooth, fibrillose, squamulose, grainy or velvet-like.
- Location of stipe: central, lateral or eccentric.
The insertion of the stipe within the cap is one of the main characters to observe in carpophores of
the family Agaricaceae. For certain carpophores, there is a continuation of the flesh between the
cap and stipe and it is very difficult to separate both entities; the stipe and the cap are confluent.
However for some other species, cap and stipe are easily separable, flesh of both the cap and the
stipe being completely different from each other.
GENERAL FORM OF THE STIPE
Flared
Tapered at apex
Clavate or club-shaped
Cylindrical / equal
Swollen
Obese
Rooting
Bulbous
Excentric
d).- Volva, ring and veil.
The young carpophore is often surrounded by one or two veils. The first one is an outer veil (or
universal veil) that surrounds the entire fruiting body. When the carpophore grows up and
strengthens, the veil will come apart leaving a volva at the stipe base and fragments of the veil will
remain on the cap surface. The second one is an inner veil (or partial veil) that covers the
hymenium from the top of the stipe to the margin of the cap. The hymenium is concealed in this
veil. When the veil breaks apart, small part of it remains on the mature fruiting body as a ring
surrounding the top of the stipe. Some traces of veil often also remain on the cap edge. In species
of Cortinarius, Inocybe, Hebeloma, Psathyrella.... the remnants of the veil on the cap, gills and
stipe are so fragile that they look like a spider’s web and are called cortina. However, this net is
only observable for a short period when the carpophores are still young as it disappears in the
adult stage. Only small threads are then observable on the upper part of the stipe.
Since the appearance of these remnants of veils differ among species they can help a lot in
mycological identification and classification.
The volva can be: floury, membranous, scaly, spherical or conical, bulb-shaped, cylindrical,
fleeting or persistent.
The ring can be: single or double edged, fixed or mobile, funnel-shaped, scaly, floury, grainy or
skirt-like... The ring may be persistent or on the contrary can entirely disappear which makes
identification even more difficult.
e).- Flesh.
- Structure: can be fibrous, grainy, cartilaginous, hard or flabby, compact or spongy, leathery
(tough), viscid, hygrophanous...
- Colour: flesh colour and notably the change in colour when the flesh is just cut are important to
observe for identification. The colour can vary with climatic conditions.
- Smell: fungi should be smelt when just collected; the smell can still be tested in fungi that are
well preserved. Smells resemble fresh flour (Calocybe gambosa, Entoloma lividum, Tricholoma
tigrinum o pardinum); aniseed (Agaricus sylvicola, Clitocybe odora); phenol (Agaricus
xanthoderma); garlic (Lepiota cristata, Marasmius alliaceus); bitter almonds (Hygrophorus
agathosmus); chlorine (Mycena alcalina); radish (Hebelomas); crude potatoes (Amanita citrina) or
be fetid (Russula foetida).
- Taste: can be sweet, bitter, prickling, pleasant or unpleasant.
1.3. Microscopic examination.
This is an essential part of fungal determination:
a).- Hyphae.
They are the structural unit of most fungi, particularly of filamentous fungi. Hyphae are composed
of an outer wall and a cavity (lumen); at intervals the hypha becomes divided by few or many
transverse walls and is then called septum (pl. septa).
The network of hyphae forms the hymenium. Sometimes, it forms underground hard and resistant
strands that are called rhizomes. Hyphae that do not have transverse walls are being referred to
as aseptate. Thickness of transverse walls, hyphae diameter and the presence or absence of
loops are all important characters to be observed in microscopic examination.
b).- Asci and paraphyses.
In Ascomycetes, spores or ascospores are formed inside asci (sac-like) that can be spherical,
pyramidal, globular, egg-shaped and cylindrical. Ascospores are usually 8 per ascus, less often 4
or a multiple of 8. Spore walls can be spotted using reagents such as Melzer’s and as said to be
amyloid when they become blue-grey to blackish by reaction to the iodine component of the active
agent.
Sterile elements of the hymenium of Ascomycetes are called paraphyses. Their shapes are
variable: narrow or enlarged at the tip, etc.
c).- Basidia and Cystidia.
In Basidiomycetes, spores or basidiospores are formed on the top of club-shaped formations,
called basidia (sg. basidium). Contrarily to ascospores, produced inside an ascus without any
attachment point, basidiospores are attached to basidia through the intermediate of a sterigma.
Basidia can be bi-polar or tetra-polar and be formed of membranous walls or not (transversal or
longitudinal). For microscopic examination, it is important to observe the diameter of hyphae, the
presence or absence of membranous walls and loops.
Sterile elements of the hymenium of Basidiomycetes are called cystidia. They are usually
distinctive from basidia by their size because they are bigger and have a different morphology.
They can be: globular, bottle-shaped, smooth or prickled, spindle- or spit-shaped, have a sharp or
obtuse extremity or oxalate crystals on the apex...
d).- Hairs.
Sterile elements located on the cuticle, hymenium or stipe. Their morphology can vary. They are
frequently observed in some Ascomycetes and Gasteromycetes.
e).- Spores.
They are the organs of sexual origin in charge of perpetuating and extending the species. They
have the same role as seeds in superior plants.
- Spore colour: to get a spore-print, place the cap of the carpophore on a white (for fungi with
dark hymenium) or dark (for fungi with light hymenium) paper sheet and the stipe going through a
central hole on the paper to dip into a glass of water for 8 to 10 hours.
In reference to spore-prints, fungi can be classified into four groups:
Melanospores: black spore-print (Coprinus, Panaeolus...)
Leucospores: white spore-print (Amanita, Lepiota, Russula....)
Rhodospores: pink or salmon spore-print (Entoloma, Volvaria, Pluteus...)
Ochrospores: ochre or ferruginous spore-print (Agrocybe, Pholliota...)
The colour of the spores observed under microscope can differ from the spore-print colour. A white
spore under the microscope often appears translucent.
Spores vary in shape, ornamentation and size: spherical, oval, globular, star-shaped, polygonal,
cylindrical, ellipsoidal, helicoidal, pyramidal, tonsil-shape, reniform (kidney-shaped), citriform,
rhomb-shaped.
The surface can be smooth, rough, reticulate, warty, prickly, and can have longitudinal or
transversal walls. Spore size ranges between 3-20 μm.
1.4. Organoleptic characteristics.
Organoleptic characteristics or properties of a substance correspond to characteristics that
can be perceived directly from senses (all of them, not only sight), without using any
instruments of measurement. These are the first appearances studied and registered in
fungal examination, bearing in mind that those data vary in time and depend of the samples
origin.
On the other hand, some features such as spore size, can easily be assessed later in time, as
they can be kept in good condition for a long period. However, some characters such as smell
and colour vary tremendously with time and origin, but also with the observer’s perception
which is very subjective. For this reason reference to commonly known substances or
aliments should be made when colour, taste or smell of fungi are described.
The main organoleptic characters of fungi are:
STRUCTURE.
VISCIDITY.
HYGROSCOPY.
FLESH COLOUR.
SMELL.
TASTE.
a).- Flesh structure.
By breaking up the carpophore, the flesh becomes visible.
The flesh of carpophores can vary in structure:
Gelatinous: easily deformable, more or less elastic. e.g. Tremella mesenterica,
Exidia.
Sticky: without stable shape, as a mucous aggregate. e.g. Fuligo septica.
Grainy: crumbles easily, composed of granules. e.g. Russula, Lactarius.
Fibrous: flesh not crumbly and fibres are orientated in one direction when the flesh is
broken. For these species people are used to refer to the stipe more than the
carpophore itself. e.g. Agaricus, Amanita.
Leathery: flesh not crumbly, fibres in all directions, entirely resistant weft. e.g.
Polyporus, Trametes, Craterellus.
b).- Viscidity.
The viscid appearance of the cap cuticle is usually studied, particularly after it has been raining.
Viscid cuticle: mucous or mucilaginous appearance.
e.g. Suillus, Hygrophorus, Lactarius blenius, Hygrocybe, Cortinarius.
Dry cuticle: never with a mucous or mucilaginous appearance even by humid weather.
e.g. Agaricus.
Semi-mucous cuticle: very shiny in humid weather, that could look mucous or mucilaginous.
e.g. Boletus purpureus.
Velvety cuticle: never with a humid or viscid appearance, including in periods of high humidity
e.g. Xerocomus badius, etc.
c). Hygroscopy.
This corresponds to the change in colour and transparency of the cap weft depending on the
humidity and dryness of the atmosphere.
Hygrophanous: translucent appearance (similar to “crystal polished with emery”) in wet
climatic conditions, either concerning the all cap, or only patches and concentric zones.
e.g. Collybia, Galerina, Clitocybe, etc.
Not hygrophanous: without any change in appearance in wet climatic conditions.
e.g. Amanita, Cortinarius, etc.
d). Flesh colour.
Other than its colour in itself, it is important to observe whether the flesh colour is changing or
not when cut.
Immutable: no change of colour with time.
e.g. Boletus edulis.
Change of colour: rapid or slow, generally due to the transformation of certain substances
by fungal enzymes in the presence of oxygen.
e.g. Paxillus involutus, Agaricus, Leccinum, Agaricus, etc.
The most frequent changes of colour are:
Turning black: Leccinum, Russula,
Turning brownish-grey:
Turning red: Agaricus, Macrolepiota rhacodes, Amanita rubescens
Turning green: Lactarius
Enzymes
Colourless substrate
Oxygen
Coloured substance
Turning blue when injured: this change in colour is typical with “Boletes”. It appears while
cutting or bruising tubes and flesh (of the cap and stipe).
It can appear instantaneously (Boletus purpureus) or gradually (B. erythropus, Gyroporus
cyanescens). For certain species, stains appear in those parts that have sustained injury
(Xerocomus badius).
A compound called variegatic acid remains colorless unless it is exposed to oxygen. The cell
walls are easily broken, exposing the variegatic acid to the air. The oxygenase enzyme
converts the variegatic acid to its quinone methide, which is blue.
Enzymes
(oxygenase)
Colourless substrate
(variegatic acid)
Oxygen
Coloured substance
e). Smell.
Without a doubt, smell is one of the organoleptic characteristics the most subjective, relying
on personal sharpness of senses as well as on the use of the right description (which
combines identification and denomination) of each smell.
One should try to perceive the “fresh” smell just following the collection of a specimen,
however sometimes a second observation should be made after some hours. There should
not be any other sources of smell close to the experiment (very smelly fungi, onions, fish,
etc.).
We distinguish various smells:
None: Amanita rubescens, Amanita caesarea.
Floury: Calocybe gambosa, Clitopilus prunulus, Clitocybe
Garlic: Marasmius aliaceus, M. scorodinus.
Aniseed smell: Clitocybe odora, Agaricus arvensis, A. sylvicola.
Putrid: Phallus impudicus, Boletus satanas.
Unpleasant, not putrid: Sarcodon imbricatum.
Radish smell: Hebeloma.
Chlorine smell: Mycena alcalina.
Potato smell: Amanita spissa, A. citrina.
Acidic / unpleasent fungal: Paxillus involutus, Boletus calopus.
Pleasent fungal: Boletus edulis.
Fruity: Cantharellus cibarius, Lepista nuda.
Iodine, ink or phenol: Boletus impolitus, A. xanthoderma.
f). Taste.
This is the particular sensation that we perceive when we put a substance in contact with the
mucous membrane of the mouth and with the tongue. It is usually linked with the smell, but
not necessarily.
A distinction has to be made between taste and toxicity: for example, Amanita faloides,
deadly, has a smoothly sweet taste, and Lactarius deliciosus, edible, has a slightly pungent
taste.
As it happens with smells, when cooked the taste of a fungus can increase (Agaricus
xanthoderma, Lepista nebularis) or decrease.
None: Auricularia auricula-judeae, Tremella mesenterica.
Sweet: Boletus regius, Boletus edulis.
Piquant: Lactarius piperatus.
Bitter: Tylopillus phelleus
Pungent: Lactarius controversus, muchas Russula
Aromatic, pleasant: Agaricus campestris.
Salty: Fistulina hepatica.
When firstly observed, the external or macroscopic characteristics of fungi are the first details
noticed. In the past, they were the basis for classification and were and are still very important
in order to know and classify the species that we study.
Two groups of macroscopic characteristics can be distinguished:
MORPHOLOGICAL:
Referring to details concerning the form and external structure.
ORGANOLEPTIC:
In reference to characteristics that can be perceived by senses
(and not exclusively by sight).
g). Fungi appearance or general shape.
The appearance or general shape is the first external macroscopic detail to be focus on. Very
often, it is not easy to describe the general shape of a fungus, because a high number of them are
different from the typical umbrella shape. This form, in reality, is only observed within the
“Agaricomycetideae” (former “Agaricales”) and some “Aphyllophorales” and “Ascomycetes”.
For example, the appearance of “inferior” fungi is difficult to describe, since these fungi are
composed of masses of mycelium without a classic fruiting body.
In summary, we can say that the “macromycetes” and higher fungi or “carpophores” present a
substantial diversity in shapes and appearances, and it is impossible to distinguish a
common external feature among the different species. The only commonly shared
characteristic in the Kingdom of fungi is a microscopic characteristic: the presence of
hyphae.
h). Colour and size.
To get an idea of the tremendous variety of colours in the world of fungi, one should bear in
mind that in Europe only nearly 2,000 species of “macromycetes” have been recorded, and as
many as 100,000 species in the world.
Considering this volume of species, it is impossible to talk about one predominant colour.
Many colours exist for fungi:
white (Agaricus, Amanita)
yellow (Tremella)
black (Tuber)
orange (A. caesarea)
grey (Tricholoma terreum)
red (A. muscaria)
green (A. phalloides, R.
virescens)
purple, garnet-red (Russula)
The only noticeable characteristic is that, in general, the mycelium always present a whitish
grey coloration, although for certain species it can be coloured (Chlorosplenium
aeruginascens bluish green, Armillaria mellea with black rhizomorphs, etc.).
The size of fruiting bodies varies enormously: from the microscopic dimensions of moulds
and “Myxomycetes” to the huge dimensions of Langermannia gigantea which measures up to
50 cm and weighs up to several kilograms.
Example of Langermannia gigantea