fungus (plural fungi) is a eukaryotic
that digests its food
externally and absorbs the nutrient
into its cells.
Along with bacteria,
fungi are the primary decomposers
of dead organic matter in most terrestrial ecosystems.
Many fungi have important symbiotic
relationships with many other organisms. Mycorrhizal
symbiosis between plants
and fungi is particularly important; over 90% of all plant species engage in
some kind of mycorrhizal relationship with fungi and are dependent upon this
relationship for survival. Fungi are
also used extensively by humans: yeasts
are responsible for fermentation
of beer and bread,
farming and gathering is a large industry in many countries.
branch of biology
involving the study of fungi is known as mycology.
were originally classified as plants,
however they have since been separated as they are heterotrophs.
This means they do not fix their own carbon through photosynthesis,
but use carbon fixed by other organisms for metabolism.
Fungi are now thought to be more closely related to animals
than to plants, and are placed with animals in the monophyletic
group of opisthokonts.
For much of the Paleozoic
Era, the fungi appear to be aquatic. The first land fungi probably appeared in
right after the first land plants appeared, even though their fossils
are fragmentary. Fungi absorb their food while animals ingest
it, and their cells have cell
walls. For these reasons, these organisms are placed in their own kingdom,
Fungi are a monophyletic
group, meaning all varieties of fungi come from a common ancestor. The monophyly
of the fungi has been confirmed through repeated tests of molecular
phylogenetics; shared ancestral traits include chitinous
cell walls and heterotrophy by absorption, along with other shared
the Fungi is in a state of rapid flux at present, especially due to recent
papers based on DNA comparisons, which often overturn the assumptions of the
older systems of classification. There is no unique generally accepted system at
the higher taxonomic levels and there are constant name changes at every level,
from species upwards. Web sites such as Index
define preferred up-to-date names (with cross-references to older synonyms), but
do not always agree with each other or with names in Wikipedia in its various
major divisions (phyla)
of fungi are mainly classified based on their sexual reproductive
structures. Currently, five divisions are recognized:
are commonly known as chytrids. These fungi produce zoospores that are
capable of moving on their own through liquid menstrua by simple flagella.
are known as zygomycetes and reproduce sexually with meiospores called
zygospores and asexually with sporangiospores. Black
bread mold (Rhizopus stolonifer) is a common species that belongs to
this group; another is Pilobolus,
which shoots specialized structures through the air for several meters.
Medically relevant genera include Mucor, Rhizomucor, and Rhizopus. |
of the Glomeromycota
are also known as the arbuscular
mycorrhizal fungi. Only one species has been observed forming zygospores;
all other species only reproduce asexually. This is an ancient association,
with evidence dating to 350 million years ago. |
commonly known as sac fungi or ascomycetes, form meiotic spores called
ascospores, which are enclosed in a special sac-like structure called an ascus.
This division includes morels,
as well as single-celled yeasts
and many species that have only been observed undergoing asexual
reproduction. Because the products of meiosis are retained within the
sac-like ascus, several ascomyctes have been used for elucidating principles
of genetics and heredity (e.g. Neurospora
of the Basidiomycota,
commonly known as the club fungi or basidiomycetes, produce meiospores
on club-like stalks called basidia.
Most common mushrooms
belong to this group, as well as rust
(fungus) and smut
fungi, which are major pathogens of grains. |
molds and slime
molds have traditionally been placed in kingdom Fungi and are still studied
by mycologists, they are not true fungi. Unlike true fungi, the water molds and
slime molds do not have cell walls made of chitin.
In the 5-kingdom
system, they are currently placed in kingdom Protista.
Water molds are descended from algae, and are placed within the phylum Oomycota,
within the Kingdom Protista.
may be single-celled or multicellular. Multicellular fungi are composed of
networks of long hollow tubes called hyphae.
The hyphae often aggregate in a dense network known as a mycelium.
The mycelium grows through the medium on which the fungus feeds. Because fungi
are embedded in the medium in which they grow, they are often not visible to the
fungi lack true organs, the mycelia of ascomycetes and basidiomycetes may become
organized into more complex reproductive structures called fruiting
bodies, or sporocarps, when conditions are right. "Mushroom"
is the common name given to the above-ground fruiting bodies of many fungal
species. Although these above-ground structures are the most conspicuous to
humans, they make up only a small portion of the entire fungal body. Some fungi
which are underground root-like structures that provide support and transport
nutrients from the soil to the rest of the mycelium.
A fungus of the species Armillaria ostoyae may be the largest organism on the planet. It was discovered in the Malheur National Forest in Oregon, and its underground mycelial network covers an area of 8.9 km˛ (2200 acres). Whether or not this is an actual individual organism is disputed: some tests have indicated that they have the same genetic makeup , but this does not exclude its being a clonal colony of numerous smaller individuals.
may reproduce sexually or asexually. In asexual
reproduction, the offspring
are genetically identical to the “parent” organism (they are clones).
reproduction, a mixing of genetic
material occurs so that the offspring exhibit traits of both parents. Many
species can use both strategies at different times, while others are apparently
strictly sexual or strictly asexual. Sexual reproduction has not been observed
in some fungi of the Glomeromycota
These are commonly referred to as Fungi imperfecti or Deuteromycota.
and other unicellular fungi can reproduce simply by budding,
or “pinching off” a new cell. Many multicellular species produce a variety
of different asexual spores that are easily dispersed and resistant to harsh
environmental conditions. When the conditions are right, these spores will germinate
and colonize new habitats.
reproduction in fungi is somewhat different from that of animals or plants, and
each fungal division reproduces using different strategies. Fungi that are known
to reproduce sexually all have a haploid
stage and a diploid
stage in their life cycles. Ascomycetes and basidiomycetes also go through a dikaryotic
stage, in which the nuclei
inherited by the two parents do not fuse right away, but remain separate in the
hyphal cells (see heterokaryosis).
zygomycetes, the haploid hyphae of two compatible individuals fuse, forming a zygote,
which becomes a resistant zygospore.
When this zygospore germinates, it quickly undergoes meiosis,
generating new haploid hyphae and asexual sporangiospores.
These sporangiospores may then be distributed and germinate into new
genetically-identical individuals, each producing their own haploid hyphae. When
the hyphae of two compatible individuals come into contact with one another,
they will fuse and generate new zygospores, thus completing the cycle.
ascomycetes, when compatible haploid hyphae fuse with one another, their nuclei
do not immediately fuse. The dikaryotic hyphae form structures called asci
(sing. ascus), in which karyogamy
(nuclear fusion) occurs. These asci are embedded in an ascocarp,
or fruiting body, of the fungus. Karyogamy in the asci is followed immediately
by meiosis and the production of ascospores. The ascospores are disseminated and
germinate to form new haploid mycelium. Asexual conidia
may be produced by the haploid mycelium. Many ascomycetes appear to have lost
the ability to reproduce sexually and reproduce only via conidia.
reproduction in basidiomycetes is similar to that of ascomycetes. Sexually
compatible haploid hyphae fuse to produce a dikaryotic mycelium. This leads to
the production of a basidiocarp.
The most commonly-known basidiocarps are mushrooms, but they may also take many
other forms. Club-like structures known as basidia
generate haploid basidiospores
following karyogamy and meiosis. These basidiospores then germinate to produce
new haploid mycelia.
often inconspicuous, fungi occur in every environment on Earth
and play very important roles in most ecosystems.
Along with bacteria, fungi are the major decomposers
in most terrestrial (and some aquatic) ecosystems, and therefore play a critical
role in biogeochemical
cycles and in many food
fungi are important as partners in symbiotic
relationships with other organisms, as mutualists,
as well as in symbiotic relationships that do not fall neatly into any of these
categories. One of the most critically important of these relationships are
various types of mycorrhiza,
which is a kind of mutualistic relationship between fungi and plants, in which
the plant's roots are closely associated with fungal hyphae and other
structures. The plant donates to the fungus sugars and other carbohydrates that
it manufactures from photosynthesis, while the fungus donates water and mineral
nutrients that the hyphal network is able to find much more efficiently than the
plant roots alone can, particularly phosphorus.
The fungi also protect against diseases and pathogens and provide other benefits
to the plant. Recently, plants have been found to use mycorrhizas to deliver
carbohydrates and other nutrients to other plants in the same community and in
some cases can make plant species that would normally exclude each other able to
coexist in the same plant community. Such mycorrhizal communities are called
"common mycorrhizal networks". Over 90% of the plant species on Earth
are dependent on mycorrhizae of one type or another in order to survive, and it
is hypothesized that the presence of terrestrial fungi may have been necessary
in order for the first plants to colonize land.
are formed by a symbiotic relationship between algae
(referred to in lichens as "photobionts")
and fungi (mostly ascomycetes of various kinds and a few basidiomycetes), in
which individual photobiont cells are embedded in a complex of fungal tissue. As
in mycorrhizas, the photobiont provides sugars and other carbohydrates while the
fungus provides minerals and water. The functions of both symbiotic organisms
are so closely intertwined that they function almost as a single organism.
insects also engage in mutualistic relationships with various types of fungi.
Several groups of ants cultivate various fungi in the Agaricales
as their primary food source, while ambrosia
beetles cultivate various kinds of fungi in the bark of trees that they
fungi are parasites on plants, animals (including humans),
and even other fungi. Pathogenic fungi are responsible for numerous diseases,
such as athlete’s
foot and ringworm
in humans and Dutch
elm disease in plants. Some fungi are predators
which they capture using an array of devices such as constricting rings or
have a long history of use by humans. Many types of mushrooms
and other fungi are eaten, including button
mushrooms, and oyster
mushrooms. Of course, many species
of mushrooms are poisonous
and are responsible for numerous cases of sickness
and death every
year. A type of single-celled fungus called yeast
is used in baking bread
and fermenting alcoholic
beverages, while mycelial fungus is used to make Shoyu
Fungi are also used to produce industrial chemicals like lactic
and even to make stonewashed jeans.
Some types of fungi are ingested for their psychedelic
properties, both recreationally
and religiously (see main article, Psychedelic
of the most well-known types of fungi are the edible
mushrooms. Many species are commercially raised, but others must be
harvested from the wild. Button
mushrooms (Agaricus bisporus) are the most commonly eaten species, used in
salads, soups, and many other dishes. Portobello
mushrooms are the same species, but are allowed to grow to a much larger
size. Other commercially-grown mushrooms that have gained in popularity in the
West and are often available fresh in grocery stores include straw
mushrooms (Volvariella volvacea), oyster
mushrooms (Pleurotus ostreatus), shiitakes
(Lentinula edodes), and enoki
mushrooms (Flammulina spp.).
are many more mushroom species that are harvested
from the wild for personal consumption or commercial sale. Milk
trumpets, and porcini
mushrooms (also known as king boletes) all command a high price on the market.
They are often used in gourmet dishes.
is also a common practice to permit the growth of specific species of mold
in certain types of cheeses that give them their unique flavor. This mold is
non-toxic and is safe for human consumption. This accounts for the blue colour
in cheeses such as Roquefort
of mushroom species are toxic to humans, causing anything from upset stomachs to
to death. Some of the most deadly belong to the genus Amanita,
virosa (the "Destroying Angel") and A.
phalloides (the "Death Cap").
cramps, vomiting, and diarrhea usually occur within 6-24 hours after ingestion
of these mushrooms, followed by a brief period of remission (usually 1-2 days).
Patients often fail to present themselves for treatment at this time, assuming
that they have recovered. However, within 2-4 weeks liver
failure leads to death if untreated. There is no antidote for the toxins in
these mushrooms, but kidney
dialysis and administration of corticosteroids
may help. In severe cases, a liver transplant may be necessary (Kaminstein
2002). It is difficult to identify a "safe" mushroom without proper
training and knowledge, thus it is often advised to assume that a mushroom in
the wild is poisonous and leave it alone.
agaric mushrooms (A. muscaria) are also responsible for a large number of
poisonings, but these cases rarely result in death. The most common symptoms are
nausea and vomiting, drowsiness, and hallucinations. In fact, this species is
used ritually and recreationally for its hallucinogenic properties. However, if
it is taken in over a long period of time (regularly over more than six months),
this species might cause a temporary loss of sight, which can last from several
minutes to an hour.
fungi compete with other organisms, or directly infect them. Some of these fungi
are considered beneficial because they can restrict, and sometimes eliminate,
the populations of noxious organisms like pest insects, mites,
and other fungi, such as those that kill plants. There is much interest on the
manipulation of these beneficial fungi for the biological
control of pests. Some of these fungi can be used as biopesticides,
like the ones that kill insects (entomopathogenic
fungi). Specific examples of fungi that have been developed as bioinsecticides
fumosoroseus, and Verticillium