a bracket fungus. On the basis of this photograph this fungus is
determined to be Meripilus giganteus (Giant Polypore).
This fungus forms a compound rosette of sporing bodies, each a
brown fan-shaped cap, soft and pliable, with pores beneath. The
caps originate from a common base and each may reach 10 to 30 cm
in diameter. The upper surface is concentrically zoned light and
dark brown with radial grooves and is almost flat and covered
with fine scales. The intensity of the color is very variable.
This fungus grows at the base of trees or stumps or from
shallowly submerged roots and prefers beech (Fagus) but
can occur on Oak (Quercus).
These fungi are usually found on the sides of trees and on
fallen logs. This one is probably growing on a decomposing log
beneath the soil surface. Fungi were once classed as plants, but
they do not photosynthesize, but instead obtain nourishment from
preformed organic materials, in much the same way that animals
do. Many are saprotrophic - feeding off
decomposing organic remains, such as dead wood. Some are
parasitic and may feed off the living tissues of plants (and
sometimes animals). Others exist in harmonious symbiosis with
organisms that can photosynthesise. Most trees require such
fungal symbionts if they are to grow
properly (especially on poorer soils). These fungi associate
with plant roots, forming mycorhizae (or mycorhizas, lit.
'fungus roots', sing. mycorhiza). The body of a fungus
is an often large and diffuse mass of whitish hairlike threads
that spread through soil, rotting logs or living wood in the
case of parasites. This mass is called the mycelium. The part of the
fungus that is usually visible are the sporocarps or sporing bodies,
like those shown above. Periodically the mycelium puts out these
structures into the open to shed spores. The mycelium is made up
of fine hairlike fibers called hyphae. Hyphae have a very
large surface area to volume ratio, which makes them
exceptionally good at absorbing nutrients. The hyphae secrete
enzymes (or rely on those secreted by other micro-organisms)
into their food, digesting it and then absorbing the nutrients
with their hyphae. In the case of mycelia, the hyphae are
especially good at absorbing hard-to-get soil nutrients like
phosphorus, indeed they are much better than plant roots at
this. They give the plant roots some of these minerals in
exchange for sugars manufactured by the plant during
The diagram below shows the mycorhiza of the beech tree (Fagus sylvatica). The mycelium forms a hairlike net that en-sheaths part of the root, this is called the Hartig net. Some of these hyphae penetrate between the root epidermal cells, which form the outer layer of root tissue.
single fungus may, in this way, connect the roots of several
trees together. The roots of neighbouring trees may also
naturally graft directly together, especially if the trees
belong to the same species. Such grafted roots can exchange
nutrients and this helps the weaker trees. If a tree is felled,
the stump may regenerate (depending on the species) by putting
out new shoots. Some of the nutrients for this growth may come
from neighbouring trees through the interconnected root network.
The largest organism on Earth is thought to be a fungus, whose mycelium covers some 37 acres, is estimated to be about 700 years old and to weigh over 100 tonnes. However, it is not easy to prove whether this mycelium remains continuous or whether it has fragmented into several smaller mycelia (which would make it a clone rather than a single organism).
Some fungi can form mycorhizas with a variety of different trees, but each woodland type, such as beech, birch, oak or pine, has its own characteristic set of mycorhizal fungi. For example, the fly agaric, Amanita muscaria, will only grow under birch and pine. Likewise, each species of tree is often capable of forming mycorhizas with several different fungus species. These fungi may or may not contribute to leaf litter decomposition, but they are good at extracting nutrients like phosphate. Brushing aside the leaf-litter in a beechwood will reveal the tiny feeder roots that protrude vertically into the leaf-litter and these coral-like roots are the mycorhizas.
Orchids characteristically form mycorhizas of a type called endomycorhizas - in this type there is no external hyphal sheath, or Hartig net, around the root, and the fungal hyphae penetrate and internally invade the cells in the outer layers of the root. Deeper in the root is a zone in which cells are digesting the fungal hyphae and the central zone is fungus-free. These fungi can digest cellulose and lignin (present in plant remains) and the relationship appears a complex and unsettled one. The orchids need the mycorhizas when they are young germlings and seedlings. The seeds will not germinate without their fungal partner, however, sometimes the fungus infects and consumes the seed, destroying it. This illustrates how these mutualistic symbioses cover a spectrum of relationships, with the fungus parasitising the plant on one hand, and the plant eating the fungus on the other. Some orchids are non-photosynthetic and lack green chlorophyll and these depend on their fungal partner to provide them food throughout their life. In contrast to the mycorhizas of trees, in which the fungus provides minerals and the plant sugars, in orchid mycorhizas the fungus appears to be supplying the plant with sugars by digesting cellulose. In this way many orchids are able to feed saprotrophically as well as photosynthetically. Many other herbaceous plants rely on mycorhizas, but mycorhizas tend to be absent from grassland.
the growing tip of a fungal hypha. Hyphae grow at their tips.
The fungus 'cell' is really a giant cell with many nuclei,
though in some fungi cross-wall partitions occur at intervals
along the hypha. The hypha is surrounded by a hyphal wall. the
growing tip is rich in vesicles, which either bud from the Golgi
apparatus (dictyosomes) if these are present, or else directly
from the endoplasmic reticulum. Many of these vesicles fuse with
the cell-surface membrane at the hyphal tip and discharge their
cargo by exocytosis, which will include materials to extend the
cell wall as the hypha grows. The vesicles also add to the
Behind this zone is a region of intense metabolic activity - rich in ribosomes that synthesise proteins and mitochondria that provide the hypha with power.
Further from the tip, vacuoles of increasing size become increasingly numerous and large lipid bodies which store fuel.
The middle zone, rich in ribosomes, may be much longer than illustrated here.
Fungi (properly pronounced 'fun-gee' with a hard g as is 'geyser') take a very different approach to the cellular animals and plants, in that they build bodies from hyphal filaments. The hyphae often have cross-walls, with pores connecting the cytoplasm on either side, and so can in this case be considered as chains of cellular units. However, although we sometimes refer to fungal cells, with the exception of the cellular yeasts, it is not always easy to say what exactly a fungal 'cell' is: is it a hypha or one unit in a hypha partitioned by cross-walls.
a cross-section through part of stalk is made up of columns of
hyphae, of variable size, packed together. In cross-section
these hyphae resemble the parenchyma cells of plants, but
longitudinal section are shown to be long filaments, unlike parenchyma, and so are sometimes called pseudoparenchyma. This is an interesting alternative approach to building a body - building it from filaments. These sporing or fruiting bodies, such as toadstools, enable spores to be released above the boundary layer of still air that coats solid surfaces. In air the boundary layer is generally much thicker than in flowing water. In water microscopic filaments or biofilms may be sufficient
to break the boundary layer.
One of the most remarkable things about fungi is their hardiness. Fungi have been able to colonise extreme environments, such as inside rocks in the extremely cold and dry Antarctic deserts (the driest places on Earth) and the inside of fuel tanks. Even the mildew that may grow on walls and other damp surfaces seems to grow well with remarkably little. Many fungi are colonisers, some are adapted to grow on burnt soil in forests, and their spores will only germinate in high temperatures. Lichens can grow on bare rocks, even on wind-blasted and salty rocks that line the upper shores. Lichens are remarkable composite organisms - composed of two very different organisms growing in a single body. One is the fungus, the other is a photosynthetic cyanobacterium or a eukaryotic alga.
This bracket fungus, growing on an oak tree, is probably Ishnoderma resinosum or a related form, as it has the right shape and colour and characteristically yields drops of red resin (click photos to enlarge, the droplets are visible as spots). However, this fungus is said to grow on dead stumps from September to December, but here it is in June on a living oak tree. Of course it could be feeding off dead wood that is part of the tree.
Above: Daldinia (probably Daldinia concentrica) otherwise known as King Alfred's Cakes. This fungud grows on ash and occasionally on other deciduous trees. Here it is growing on a fallen branch, which does look like ash. The sporing body can be up to 5 cm (2 inches) across. Also sporulating on this log was a myxomycete or plasmodial slime mould.
brackets on a living oak tree.
Types of Fungi
Fungi are classified scientifically into several groups and can also be classified more commonly by
general appearance. Scientifically we recognise three major divisions: 1) zygomycetes, 2) ascomycetes, and 3) basidiomycetes.
1) The zygomycetes are the simplest of the true fungi, and many moulds belong to this group (moulds can also be bacterial or protoctistan in origin, see classification of organisms). These moulds consist of spreading masses of feeding hairlike-hyphae (the mycelium) and vertical aerial hyphae, such as the sporangiophores, bearing sporing bodies/capsules (sporangia, sing. sporangium) which contain a mass of spores. The mycelium consists of branching hyphae that generally lack dividing cross-walls (they are aseptate), so that they are multinucleate and the protoplasm is undivided. Cross-walls do form in old colonies, however, where they wall off dead air-filled hyphae from the still living hyphae.
Reproduction in Zygomycetes
Bread mould, Mucor, is a common example. Mucor is heterothallic, meaning it exists in two body types (heterothallic = more than one 'body' or thallus type) which are physically identical but of different sexual compatibilities: the + (plus) type of mycelium can only mate with a - (minus) type of mycelium and vice versa - mycelia of like types can not mate. Each spore produces either a plus-type or a minus-type mycelium, upon germinating. Each mycelium produces minute, more-or-less spherical, asexual sporangia, borne on sporangiophore stalks and the asexual spores are of the same genetic type as the parent mycelium (they are genetic clones of the parent). A hemispherical cross-wall, called the columella, forms the wall of the sporangium and divides the sporangiophore stalk from the sporangium.
Above: part of a Mucor mycelium magnified, showing an erect aerial and asexual sporangiophore bearing a spore-containing spherical sporangium. These sporing structures give the zygomycetes their common name of pin-moulds. The sporangium is about 100 micrometres in diameter.
may be primarily by wind or water, though the role of animals
should not be underestimated. Wind-dispersed
such as Mucor
the outer surface of the
sporangium is studded with spikes of calcium oxalate, which make the surface water-repellent, keeping it dry. When ripe, the sporangial wall ruptures and breaks apart, exposing the dry, powdery spore mass which can be dispersed by air currents. Most species of Mucor, however, rely primarily on rain-splash to disperse their spores. In these species, such as Mucor hiemalis and Mucor ramannianus, the sporangial wall dissolves, but it does not reveal a dry powdery mass of spores, instead the spore mass expands as it takes up water, forming a slimy sporangial drop, larger than the original sporangium. The slime dries, leaving the spores cemented to the columella. These spores cannot be easily blown away by the wind, but can be scattered by falling rain drops (an example of the use of gravitational potential energy to
disperse spores). Splash-dispersal of this type is short-range, scattering the spores up to one metre from the parent sporangium.
Some pin-moulds that rely on rain-splash to disperse the sporangial spores, produce secondary asexual structures as side-branches branching off the main sporangiophore. Each branch ends in a small secondary sporangium, or sporangiole, containing a few spores (4 spores per capsule in Thamnidium elegans). These sporangioles are small and very light and detach easily to be blown away by the wind. Cunninghamella only produces one type of asexual sporangium, called conidia (sing. conidium). These are interpreted as tiny sporangia, each containing only a single spore. Conidia are borne on single or branched aerial hyphae called conidiophores. Conidia easily detach to be blown away.
Each spore inside the sporangium contains one or more nuclei and each may germinate under certain conditions to form a daughter colony which is genetically identical to that of the parent. Both the parent and asexually produced daughter colonies are haploid (that is they contain only one set of chromosomes).
The mating-type is determined by a single gene with two alleles (versions of a gene), one for plus, the other for minus. If a plus-type (+) encounters a minus-type (-) then mating and sexual reproduction may occur. (Some mycelia may be neutral and these do not mate with either + or - types). When close, but not touching, the fungi sense the presence of the compatible other and both produce a type of aerial hyphae, called zygophores, which arch over towards the neighbouring mycelium. Each mycelium-type secretes its own mating hormone and this hormone triggers mycelia of the opposite type to produce trisporic acid. Two neighbouringh mycelia produce enough trisporic acid to trigger zygophore synthesis. Once synthesises, another set of volatile chemical messengers are produced, which diffuse through the air and stimulate the zygophores to grow towards the colony of opposite type (a process called zygotropism; tropism being growth in a specific direction triggered by a stimulus). When zygophores of neighbouring colonies rub against one-another (or at least come in close proximity?) they develop sexual structures. They often rub together on one side and here they produce lateral swellings, called progametangia (sing. progametangium). As the progametangia develop, a wall-partition grows, closing off a multinucleate mass of protoplasm in the end of each progametangium, this multinucleate compartment being called the gametangium (plural gametangia). Where the neighbouring plus-gametangium and minus-gametangium meet, their end walls break down and the protoplasts of the gametangia fuse into a single protoplasmic unit, which is the young zygospore. Plus and minus nuclei fuse in pairs within the young zygospore which becomes encased in a tough shell or coat when mature and is now called the zygospore (or zygosporangium). The zygospore is a resting stage, and after a period of dormancy it is able to germinate. A hypha emerges which develops into an aerial hypha, a sporangiophore bearing a spore-capsule at its tip called the germ-sporangium. This ruptures to release haploid spores which are all either plus or all minus (in some other zygomycetes, spores of both types are produced).
Left: two progametangia borne on hyphae of compatible colonies growing toward one-another. In the case of mucor, the progametangia are borne on zygophores (aerial hyphae). In other forms they are simply short upright structures that grow together like a pincer from mycelial hyphae. In forms capable of self-fertilisation, the two aerial hyphae are borne on the same parent hypha.
Gametangia develop where the progametangia meet. Subsequently the dividing walls between the two gametangia break down and the protoplasts of the two gametangia fuse. At least some of the haploid nuclei fuse in pairs, forming diploid nuclei.
The fusion cell formed by the fusion of the two gametangia is the zygospore, which develops a black and warty outer wall, which is impregnated with melanin and sporopollenin. (Sporpollenin is also found in the walls of the pollen grains of plants). The zygospore wall is very impermeable and resistant. The zygospore protoplasm is rich in glycogen and lipid food reserves.
The zygospore is not a dispersive spore, but a resisting spore and does not germinate immediately. When conditions and/or timing are right and it does germinate, it gives rise to a germ tube which develops into an aerial sporangiophore, capped by a germ-sporangium. The germ-sporangium contains haploid spores, produced by meiosis. In Mucor, all the spores in a given germ-sporangium are of the same mating type (+ or -) though in some forms they may contain both mating types (or all three if a neutral type is also formed). This suggests that usually only one of the 4 haploid nuclei produced by meiosis survives. The spores of the germ-sporangium are dispersed and germinate to produce haploid mycelia of a given mating type.
is readily seen in Zygomycetes such as Phycomyces. The core of
protoplasm in the centre of the hyphae undergoes rapid streaming
at 20-40 micrometres per second. This rapid streaming is similar
to the protoplasmic streaming seen in plant cells, but different
in origin. In the fungal hypha it is driven by evaporation
(transpiration) of fluid from the growing aerial hyphae - hyphae
growing rapidly upwards to form sporangiophores. It is toward
these aerial hyphae that the streaming eventually terminates,
and such streaming presumably helps deliver the materials needed
by these rapidly growing hyphae. In addition, however, there is
much slower streaming of the cylinder of protoplasm in the
hyphal periphery, adjacent to the cell membrane and wall. This
slower streaming may be in the opposite direction to the main
streaming and is probably driven by the cytoskeleton, as is the
streaming in plant cells. Aerial hyphae initially grow at their
tips (apical growth), but then this growth pauses as the
aporangium begins to form and then extension of the hypha
continues as it grows beneath the sporangium (sub-apical
Another example of a zygomycete is Pilobolus kleinii which grows as a tiny hairy mould on cow-pats. This mould produces tiny aerial sporangiophores (each 5 mm or so in height) which bear a terminal swelling, about 1 mm long, which functions as an eye. On top of the eye is a dark spore mass, inside a black capsule (sporangial wall) forming the sporangium. Inside the eye is a lens and beneath it, in the adjoining sporangiophore is a yellow-orange doughnut-shaped ring, which is the light-sensitive retina. The lens focuses incident sunlight onto one spot on the retina, allowing the fungus to accurately determine the direction of the light source. (The mould has no brain and the eye does not serve in image formation,
merely as a light-direction sensor). The sporangiophore bends towards the light and when ready the black sporangium cap and its enclosed spore mass are jettisoned, being fired up to about 2 metres into the air! This disperses the spores clear of the cow pat, into the grass where they may be eaten by a cow and pass through to germinate on a fresh cow-pat.
Above: Pilobolus, showing four sporangiophores terminating in the eye-like structure with
anatomy of a toadstool sporocarp (using a 3D computer model
rendered in Pov-Ray). The cap
contains gills: flat plates of soft
tissue bearing characteristic cells called basidia (singular basidium).
Each basidium initially bears four black spores (basidiospores).
These spores are fired away from the gill surface to a distance
of 0.1 to 0.3 millimetres and once clear of the gill they then
fall from the cap, in-between the gill plates, under gravity.
Spore discharge is accompanied by shedding of a drop of liquid
from the spore and a weakening of the join connecting the spore
to its basidium. Additionally either surface tension forces
and/or electrostatic repulsion are thought to propel the spores
from the gill surface. The stipe
holds the cap a few centimetres above the surface, placing it
above the most stagnant layer of air (stagnant boundary layer)
which is typically a few centimetres, so that when the spores
fall free of the cap they are caught by turbulent air and
carried away and dispersed by the wind.
The annulus is a disc of tissue where the cap, originally a sphere in the young button-mushroom stage, was attached to the stipe. When the cap ripens and expands into its umbrella shape, it tears free of the stipe, leaving the annulus where the breakage occurred. The cap then continues to expand as it straightens out. Extending from the base of the stipe, into the substrate/soil are fine branching strands, called mycelial strands, which are bundles of hyphae. Mycelia often explore the substrate as mycelial strands and fan out into feeding hyphae where they encounter a food source. Bundling into mycelial strands helps the mycelium cover larger distances as it grows, and also provide stronger anchorage points for the sporocarp. The strands are also good at conducting nutrients over large distances from one part of the mycelium to another. The toadstool is short-lived, lasting a few days. Its light construction is ideal for its function. Click the thumbnails below for full-size unlabeled versions of the toadstool model.
a vertical section through a mushroom gill (computer model). The
gill comprises a sheet of vertical hyphae, called the trama. Either side of this
is a sheet of convoluted hyphae, called the sub-hymenium, which are
more-or-less horizontal and so appear as pseudo-parenchyma in section (that as
sections through the width of the hyphae make it appear as if
they are rounded cells, or parenchyma, when they are actually
hyphal threads). Outermost are two layers of paraphyses
hairs) with spore-bearing basidia
dispersed among them (in a hexagonal arrangement when the gill
is seen face-on, typically with six paraphyses around each
basidium, bottom right) forming the hymenium. Each basidium
produces four basidiospores, each of which is borne on a small
stalk (sterigma). When discharged the
spores are fires out sideways in this perspective, before
falling down under gravity. in at least some spaces, it is known
that the sterile paraphyses are in fact developing basidia. The
gill is about 150 micrometres thick and each pair of gills are
about 100 micrometres apart. Large cells, called cystidia (sing. cystidium, not
shown) emerge from the hymenium at intervals and span the gap
between neighbouring gills and serve to keep the gills apart, so
that the spores can fall freely.
Below: a section through the gills of the mushroom Agaricus (permanent preparation, stained and fixed).
Boletes, such as Boletus, are toadstools in
which instead of gills, the cap has vertical tubes, each
opening by a pore on the underside of the cap. The spores fall from these pores.
2) Bracket Fungi (Shelf Fungi)
Basidiomycetes that grow attached to wood. Some are parasites growing and feeding on living trees.
Others grow on and feed off dead wood, which they help to rot. Sometimes they grow on buried logs and
may then emerge upright as large leathery trumpet-shaped structures that superficially resemble
toadstools. The sporocarps are tough, leathery or woody in texture and may live for 10 years in some
species; they are often large. They are often semicircular and protrude from the log or branch to which
they are attached, like brackets. They have no, or a very short, stalk. Pores on the underside release
spores, which fall under gravity to be dispersed by the wind. Growing attached to wood, they are
naturally elevated above the ground, often at considerable heights if the host tree is still standing, and
so need no stalk to lift them above the still air layers. Some species of bracket fungi are circular (an may
have short stalks) and do not project but are pressed against the wood. In this instance the spores are
released from the upper surface.
3) Stomach fungi
These basidiomycetes are also descriptively called gasteromycetes (literally: 'stomach fungi') and their
sporocarps are sac-like. A well-known example are the puffballs. Puffball sporocarps consist of spongy
sacs full of spores. The spores are produced by brown tissue, called gleba, inside the sac and which is
readily visible if a ripe puffball is cut open. There is a single large circular pore, or sometimes a tear, in
the top of the sac. When rain drops hit the sac, they deform it slightly, causing a dense cloud of spores
to be pumped out through the pore (think of a pair of bellows) to a height clear of the stagnant boundary
layer of air. The puffball is elastic and returns to its previous shape, until the next rain drop strikes it. The falling rain drops provide the energy to disperse the spores, which is due to gravity again. Giant
puffballs may be up to 40 cm (16 inches) across and can produce seven million million spores! In the
giant puffball, the spores are released from a tear.
Earth stars are another example of a gasteromycete. Like puffballs, these are sacs of spores and have
one or more pores in the top. The spores are also dispersed by rain-drops, but earthstars can also
move! Leaf-shaped structures or valves close around the sac in dry weather, protecting it and its spores, and open when wet to allow spore dispersal. These movements are passive and due to tensions set up in the tissues which expand to different degrees when wet, expanding most on the outside, causing the valves to open.
Also belonging to the gasteromycetes are the bird's nest fungi (Cyathus and Crucibulum) in which the
sporophore consists of a cup or open vase, about 1 centimetre in diameter, and containing disc-like
bodies (peridiola, sing. peridiolum) or 'eggs' attached to the inner wall of the cup by a small stalk
(funiculus). The whole resembles a tiny bird's nest full of eggs. They occur on rotting wood but Cyathus
stercoreus occurs on herbivore dung. The dispersal mechanism is also splash dispersal - large
raindrops striking the inside of the cup are broken into smaller droplets and reflected out of the cup,
often carrying a peridiolum with them for a distance of up to one metre from the cup. The stalk breaks
away from the cup easily and accompanies the peridiolum. The stalk is sticky and attaches the
peridiolum to an object it lands upon. Each peridiolum consists of a wall of hyphal tissue surrounding
gleba (a mass of small chambers separated by tramal tissue and lined by basidia). The hyphae in the
wall may grow out and establish a new colony asexually, but if the peridiolum of Cyathus stercoreus is
eaten along with vegetation by a herbivore, then the basidiospores pass through and germinate on the
Sphaerobolus forms tiny cups, only 1-2 millimetres in diameter, containing a single 'egg' or glebal mass
about 1 millimetre in diameter.The cup has two linings, joined at the rim, so that it is like one cup inside
another. The cup is designed to dry out in such a way that strains are set up, until the inner cup
suddenly flips out, bulging up and propelling the glebal mass several metres! The hyphal in the glebal
mass may produce a new mycelium asexually, or sometimes from the basidiospres. Often a new
mycelium grows from large asexual spores called gemmae, which are also present in the glebal mass.
Again, this fungus may perhaps also be dispersed by herbivores eating the glebal mass and passing te
spores out with their faeces.
and below: The bird's nest fungus, e.g Cyathus, Crucibulum. The 'nest' or cup
structure is about 1 cm across and the 'eggs' are the
peridiola - the gleba divides into these masses during
development and each peridiolum is encased in a firm wall of
interwoven hyphae. Each peridiolum is attached to the inner cup
wall by a hyphal thread called the funiculus. Rain drops
striking the cuip scatter off its inner surface and the larger
droplet fragments may carry away a peridiolum up to a meter or
so from the 'nest'. The funiculus is sticky and will entangle on
any object that it strikes on its projectory. Some of these
fungi, e.g. Cyathus
live on herbivore dung, and if the periodiolum comes to rest on
grass it may be eaten by a herbivore and pass out in the dung,
in which case the basidiospores will germinate with a ready-made
food source! Other forms grow on rotting wood and sometimes new
colonies are established by the growth of the hyphal case of the
peridiolum, without basidiospores germinating.
Images courtesy of Nicholas Money, Professor of Botany at Miami University. Prof. Money is an expert on fungal movement and spore dispersal.
horns and cage fungi
These basidiomycetes are varied in shape, but many, such as Phallus, are phallus-shaped. They 'hatch'
from egg-like structures early in the morning and are covered in a sticky fluid which contains the spores
and smells like a rotting corpse. This attracts flies who carry away the sticky fluid and its spores,
dispersing them. By about midday there is no sticky fluid remaining on the stink-horn and it begins to
whither. Stink horns are classified with the gasteromycetes, as although they are not splash-dispersed,
the spores are released by tissue breakdown from a sac-like structure. In some forms, the spore-
producing body expands outwards, from a white egg-like structure, but develops into a lattice-like 'cage'.
These are the so-called 'cage fungi'.
5) Disc and Cup Fungi
The sporocarp is disc or cup-shaped in these ascomycetes. They are usually stalk-less, with the
exception of morels which consist of a wrinkled head on top of a stalk. They generally do not need
stalks, since they shoot their spores a short distance into the air (several millimetres to several
centimetres) just high enough to clear the layer of still air and enter the turbulent layer to be scattered
by the wind. The spores are fired from the upper surface of the disc, or from the inside of the cup. They
have no gills and no visible pores, but are smooth. However, the spore-releasing surface is covered by
microscopic pores. They become hard and brittle when dry, but remain alive, and fell rubbery when
moist. The ascomycete sporocarp (ascocarp) is called an apothecium when disc or cup-shaped and a
perithecium when flask-shaped.
6) Burnt Fungi
These basidiomycetes also fire their spores into the air, but resemble nodules or raised patches of burnt
and hard wood. They are black, dry and hard to the touch. They grow on rotting wood.
7) Jelly Fungi
Feel like jelly, and are often translucent (like coloured glass). They come in a variety of shapes,
including brain-like masses and ear-like lobes (e.g. Jew's ear fungus). They usually grow on rotten wood.
8) Coral Fungi
Coral fungi, e.g. Clavaria, are basidiomycetes which grow upright, often branching, and so resemble
coral, candle wicks, tiny clubs, candelabras, tiny antlers or tiny flames. The spore-producing surface
covers the end regions of the sporocarp, being exposed as it covers the external surface.
9) Encrusting Fungi
In addition to the burnt fungi, many ascomycetes and basidiomycetes are encrusting, forming velvety
films, cushions or nodules on wood and other surfaces.
These ascomycetes produce subterranean sporocarps and they belong to the discomycetes, even
though their spore-bearing surface is not open and exposed as in typical disc and cup-fungi. They seem
to rely on animals, such as rodents, finding and eating them in order to disperse them. The most prized
edible truffles belong to the genus Tuber. The truffles appear to have evolved from typical
discomycetes, and some still have a structure suggestive of a closed cup. The paraphyses form a
convoluted branching network through the ascocarp (a pseudoparenchyma) which contains spherical
asci dotted about, each ascus containing one to four spores only. The asci in truffles do not rupture to
disperse the spores.
Morels (Morchella) are ascomycetes that consist of a stalk, up to 15 cm tall, bearing a club-shaped
pitted surface, the pits being lined by asci. Like truffles they are prized by humans as food.
12) Rusts and Smuts
The rusts are basidiomycetes of the Uredinales group with over 100 genera and over 5000 species. All
are parasites of plants, being unable to grow in nature without a host (they are obligate parasites). The
smuts or Ustilaginales is another (smaller) group of plant parasites usually classed as basidiomycetes.
Fungal pathogens of plants will be considered in a separate article.
13) Water Moulds and Protofungi
The water moulds and related types, also called the oomycetes are protofungi (in a similar way that
protozoa are proto-animals and algae are protophytes). They produce aquatic spores, called
zoospores, which swim in water by means of flagella. These protofungi are grouped with the protozoa,
slime moulds and algae in the kingdom Protoctista and are no longer classified as fungi by most
14) Slime Moulds
These are no longer classified as fungi and are considered a type of protozoan or protofungus and so
included in the Protoctista. There are two chief types: cellular slime moulds, such as Dictyostelium, and
plasmodial slime moulds like Physarum. They are capable of motility, moving around slowly by crawling.
Yeasts are unicellular fungi that produce no sporocarp and typically no hyphae, occuring predominantly
as walled cells which reproduce by budding. Many yeasts are ascomycetes, but some are
basidiomycetes, whilst others have no sexual cycle and produce only asexual spores. Yeasts are
extremely common, accounting in large part for the dusty appearance of fruit like grapes (the yeast
growing on sugars that leak or exude from the grape) and some human infections. Pink films of 'mould'
are often due to yeast. More on yeast.
some mushroom graphics for general purpose use.
A number of fungi, particularly certain toadstools emit light. The light is frequently emitted by the sporocarp or spores and may attract nocturnal insects, such as moths, which disperse the spores. Sometimes the vegetative (non-sexually reproducing) mycelium luminesces. The exact functions of fungal bioluminescence are not known for certain. Luminescent toadstools are generally wood-eaters, capable of digesting lignin, a complex polymeric polyphenol which is hard to digest and extremely resistant to decay. Since bioluminescence requires a lot of oxygen (requiring a lot of ATP generated by the mitochondria) it has been suggested that this protects the fungus by consuming reactive oxygen species (ions, atoms and molecules containing an oxygen radical) produced as toxic by-products of lignin digestion. The light produced is cold light, as is typical of bioluminescence in which some 90% of the energy is dissipated as light (compare this to about 10% for a tungsten-filament light-bulb in which most of the energy is radiated as heat) and the light is green or white or whitish-green.
One of the most well-known bioluminescent toadstools in the British Isles s the Honey-Tuft (Honey) fungus, Armillaria mellea, a well-known parasite of trees which can also parasitise shrubs and herbaceous plants. In North America is to be found the famed Jack o' Lantern: Omphatolus illudens and Omphatolus olearius, formerly Clitocybe illudens, Omphatolus olearius also occurs on the European
continent where it grows preferentially on olive trees (formerly Pleurotus olearius). Although these fungi emit light bright enough to navigate by, and sometimes to read and write by, at night, others emit a much dimmer light. Some species may also have luminous and non-luminous strains and the full extent of bioluminescence in fungi is not established. So, what is the function of bioluminescence in fungi? Production of light by living organisms consumes large amounts of chemical energy and requires oxygen. The fact that it is so energetically expensive and relatively common suggests that it has a definite advantage to the fungus. In some fungi the sporing bodies emit light as long as they are shedding spores and it has been suggested that they attract night-flying insects to disperse the spores. This may well be the case in these species, but in others, including the Honey tuft fungus, it is the feeding and growing mycelium which emits light, causing rotting wood to glow. Similarly, fungal hyphae have been seen to cause rotting leaves to glow. Indeed, tree roots infected by fungi have been seen to glow. In subterranean roots the light cannot be functioning to attract spore dispersers. Another distinct possibility is that the light is acting as a signal to synchronise fungal activity and growth. Recent research suggests that light produced in deep sea sponges may perform a similar function: conveying signals from one part of the organism to another to synchronise activity during development. Cells in the mammalian body, including human cells, also respond to light and it has been suggested that infra-red light might be sued as a synchronising signal in cell-to-cell communication in mammals.
Some toadstools found on a damp grass lawn in autumn:
images to enlarge.
These toadstools were found on a damp lawn in Autumn. Marasmius forms classic 'fairy-rings' - rings of toadstools growing in a lawn, appearing in the same place each subsequent year, but age can be estimated by their diameter). They occur because as the mycelium depletes nutrients in the soil it grows outwards to colonise new soil. Boletes form mycorrhizae with trees and are grow in association with tree roots, which were presumably running beneath the lawn.
toadstools not all the gills are of the same size. All the gills
extend from the cap margin inwards, but
they are of different lengths. Typically some of the gills extend more-or-less all the way from the margin
to the stipe, these are the largest or primary gills. Between each pair of primary gills is a secondary gill,
which is shorter, extending most of the way towards the stipe, and between each primary and
secondary gill is a short tertiary gill.
Another common toadstool of lawns is the ink cap (lawyer's wig, shaggy ink cap, or shaggy mane)
Coprinus comatus. This toadstool, which may reach 30 cm in height, is unusual in that the gills, initially
white, turn pink and then black with spores as they drip black ink-like droplets from the gill-margin which
slowly dissolves. These droplets are laden with spores. This happens as the gills undergo autolysis, or
self-digestion, dissolving into liquid spore masses. They will auto-digest rapidly once picked. In most
toadstools, any given region of a gill will contain basidia in different stages of development, but in the
ink cap they develop in a definite pattern, with those at the margin of the cap being the most mature,
thus the maturing gills grade from white near the stipe, to pink and through to black at the margin. The
caps therefore dissolve from the perimeter inwards.
on Decaying Wood
Fallen tree limbs, dead trunks and stumps are valuable habitats for fungi (and in turn for the creatures
that depend on them, such as fungus-eating insects). (See Deadwood). Brown rots are caused by fungi
that digest the hemi-cellulose and cellulose components of wood, whilst leaving the lignin intact, causing
the wood to darken. White rots decompose all components of the wood, including lignin. Lignin is an especially tough compound, essentially a complex polymer of phenolic compounds, it is very resilient physically and chemically and few organism can digest it. The wood has to be moist enough to support the growth of these fungi.
Fallen limbs, stumps and dead trunks of beech trees (Fagus) support an especially rich diversity of
fungi. Some of these have a strong preference for beech wood, e.g. Pholiota adiposa, a large toadstool
with golden-yellow caps and rust-coloured spores, and which also occurs at the bases of living beech
trees. Others are more general, occurring also on the wood of other species, e.g. the sulphur-tuft
(Hypholoma fasciculare) a medium-sized toadstool of sulphur-yellow (sulfur-yellow) caps. In the final
stages, when the wood is crumbling the puff-ball Lycoperdon pyriforme can be seen growing on it (it is
unusual for puffballs to grow on wood). A beech stump takes a few years to rot away completely.
Oak (Quercus) supports fewer fungi, but some are specific to oak. Fistulina hepatica, the beef-steak
fungus, a large bracket which feels and looks like red meat and resembles meat when cut, grows on
living oaks, though it feeds on the dead heartwood. It is a brown rot, darkening the hard wood to a rich
brown colour without destroying the lignin which gives it its structure and such darkened heartwood is
prized by cabinet makers.
Birch wood decomposes especially rapidly, often leaving behind empty cylinders of bark, whilst conifer
wood tends to decompose more slowly, with yew wood persisting for many years.
on Decaying Leaf Litter
When leaves begin to senesce, whilst still on the tree, they leak materials from their aging cells, which
supports the growth of microscopic 'phylloplane' ('leaf-plane') fungi, particularly yeasts, including
basidiomycete yeasts (such as Sporobolomyces) and black yeast, which is part yeast-like, part
mycelial. These fungi initiate decomposition when the leaf falls, but larger fungi, such as toadstools
soon develop and feed on the leaf-litter (and also bacteria and invertebrates, such as insects, mites
and worms). These toadstools may be general, occurring in a variety of broadleaf and/or coniferous
woods, or they may be more specific, preferring a certain type of leaf-litter. Many toadstools growing
amongst the leaf litter are also mycorrhizae and these are often quite specific, e.g. the fly agaric,
Amanita muscaria, which is found only under birch and pine with which it forms mycorrhizae.
Eventually, only the more indigestible parts of leaves and wood litter and other organic matter remain -
the lignin (from plants), chitin (from animals and fungi) and keratin (from animals) to form humus.
(Dryad's Saddle) bracket fungi growing on an old sycamore tree
in Fredville Park. This fungus is parasitic but is also found on
stumps. This tree had lost much of its crown but was still very
much alive. It is not clear whether this fungus is growing on
the living or dead wood. This fungus is found most often on
beech, elm and sycamore.