First posted June 18, 2004* Last updated May 24, 2007
Fungi are rarely seen,
so we often think of them as rare or unimportant.
could be further from the truth:
Life on Earth could not exist
Fungi are essential
(1) proper plant root function, and
(2) breaking down dead organic material into
simple compounds that plants can absorb.
When we think of fungi, we usually think
of mushrooms, either the kind in the grocery store
or the type that grow on the forest floor after a
rain. Compared to redwoods, they are rather small,
and compared to crops like corn or wheat, they seem
insignificant and unimportant, rather a minor player,
a small, insignificant plant we can ignore.
Fungi are both important and unique.
They are important enough that life on Earth could
not exist without them, and they are so unique that
they are placed in their own Kingdom, on a classification
level equal with the classification level "Plant"
or "Animal". Far from being "small,
insignificant plants", they are essential to
our own survival and that of every plant and animal
on the planet. And they are not "plants"!
It may surprise you, but if they were not placed in
their own Kingdom and were forced to be classified
as either a plant or an animal, they would be placed
with the animals, based on biological markers of evolution.
Fungi share more molecular similarity with animals
than with plants, implying that plants evolved from
one ancestor and fungi and animals from another.
What are fungi?
Fungi are characterized by the fact
that they are generally multicellular organisms, with
a nucleus and a cell wall made of chitin (the same
material that makes up the external skeletons of insects)
and a unique mechanism of acquiring nourishment. In
distinction from plants, which make
their own food ("autotrophs", via chlorophyll),
and animals which eat food ("heterotrophs",
via eating plants or other animals), fungi neither
eat nor make food: they absorb food.
If you were a fungus and you wanted to "eat"
a chocolate cake, you would stick your fingers into
the cake, drip digestive chemicals off your fingers,
and absorb the cake directly through your skin into
your body! That is how fungi eat: they send parts
of their body (hyphae) directly into their food, secret
chemicals which helps to break the food down into
simpler molecules, and then asbsorb the food directly
into their cells.
Fungi are not rare: they are everywhere.
Just leave a piece of bread or fruit out on a plate
and see how long it takes for a colony of fungi to
grow. Compare this to plants: if you left out a tray
of soil, how long might it take for a plant to sprout?
Years? Fungi are everywhere, with billions of spores
settling out of the air all the time. They are also
present on the roots of virtually all vascular plants
(ferns, conifers, and flowering plants), which depend
on the fungi for many things.
Fungi assist plant roots
in four ways
The fungi on plant roots form an association
called mycorrhizae, a complex mutually benefical association.
The mycorrhyzae increase the surface area of the roots.
How much? One centimeter of root has about 3 meters
of hyphae, an increase in length of 300x. This increases
the surface area for the absorption of water. Ten
cubic centimeters of soil may have 1 kilometer of
fungal hyphae, having a fungal surface area of 300
square centimeters interfacing with the soil. In addition,
the fungus actively and selectively absorbs minerals
(especially phosphate ions) that the plant needs and
transfers them to the plant, while excluding minerals
that the plant does not need (sodium ions). The fungus
also secretes growth factors that stimulate root growth
and branching, as well as antibiotics that protect
the root from pathologic bacteria and pathologic fungi.
Remember, the antibiotic penicillin comes from the
common bread mold, Penicilium. The root is
just one organism growing in an underground world
of competing and hostile bacteria, fungi (there are
30,000 species of fungus that are pathological to
plants!), and animals (nematodes), so the root needs
all the help it can get. Fungi are very important
to the health, growth, and function of roots.
Fungi are the world's
most important recyclers
Fungi are also important in the recycling
of organic material and nutrients. Without fungi breaking
down dead plant and animal matter, carbon and other
molecules essential to life would be locked in organic
molecules that are too large for plants to absorb.
Fungi break down organic molecutes, which are large,
complex structures too large to pass across the cell
walls of roots, into their inorganic constituents,
such as carbon, nitrogen, and other constituents,
which are much smaller (atoms). The air is so loaded
with fungal spores, that the minute a plant or an
animal dies, it is covered with spores. The fungal
hyphae secrete exoenzymes and rapidly enter the body
of the dead animal or plant.
While we may applaud the fungi as they
rid the world of dead organic material and make those
nutrients available for re-use, it is a different
story as they destroy our food and coat our shower
curtains. It is estimates that each year fungi destroy
10% to 50% of our fruit crops, and a wood-digesting
fungi does not differentiate between a fallen limb
and a plank on a boat. During the Revolutionary War,
the British lost more ships to fungal attack than
to enemy attack. Soldiers who were stationed in the
tropics during World War II saw their tents, clothes,
boots, and some equipment be destroyed by molds.
and function of fungi
The vegetative (nutritionally active, as opposed
to the reproductive) body of most fungi is usually
hidden, being diffusely organized around and within
the tissues of the food sources. Except for yeasts,
which are unicellular, most fungi are multicellular,
composed of tiny filaments called hyphae.
The hyphae are composed of cell walls made of chitin
(the same material that makes up the external skeleton
of an insect), a cell membrane, and cytoplasm. The
hyphae form a interwoven mat called a mycelium, which
is the "feeding" network of a fungus.
The reproductive mechanisms of fungi are quite varied.
Some reproduce sexually, with some cells being haploid
(n, that is, only one set of chromosomes, like a human
egg or sperm), some diploid (2n, that is, having a
complete set of two of each chromosome, like most
cells in a human body), and some being heterokaryous
(n+n, that it, two sets of diploid chromosomes, but
not united into a complete set of two copies of each
chromosomes). Others reproduce asexually, such as
the single-celled yeast, that merely grow a miniature
yeast on their side, called a bud. This process is
Life Cycle of a Fungus
The life cycle of a fungus begins with a spore, the
reproductive body. It is like a seed, in that it grows
up into the adult organism, and, like a seed, it is
highly resistant to drying out, which would kill the
spore. Unlike a seed, which is a multicelled zygote
plus nourishment, the spore is a single cell. When
the spore starts to grow, a hypha begins to grow out
of the spore. All hyphae are only one cell wide but
many cells long. The body of a fungus is built up
out of many threads of hyphae, collectively called
the mycelium. The mycelium grows within the substance
of its food: soil, plants, animals, people, dead wood
or vegetation. When growing conditions are favorable,
the fungus sends up fruiting bodies, which we recognize
as mushrooms or other structures. These fruiting bodies
produce more spores. As noted above, fungi are so
prolific in producing spores that millions are raining
down all the time. You can't put out a piece of bread
without it being instantly colonized with fungal spores.
If you keep it moist, it will have recognizable fungi
growing on it in just 3 to 5 days.
This form of reproduction is called asexual reproduction.
Many (but not all) fungi also reproduce sexually,
but each of the four divisions of fungi have their
own unique way of doing it.
|Four types of fungi
There are four phyla in the Kingdom Fungi: chytrids
(Chytridiomycota), zygote fungi (Zygomycota), sac fungi
(Ascomycetes), and club fungi (Basidiomycetes). Mushrooms
are the reproductive structures of Basiomycetes ("basidium"
means "little pedestal"), and the yeast that
make our breads rise and our beer and wine alcoholic
are either Ascomycetes or Basidiomycetes. Let's look
at the four types in more detail.
The Primitive Fungi
These fungi are mostly aquatic, are notable for
having a flagella on the cells (a flagella is
a tail, somewhat like a tail on a sperm or a pollywog),
and are thought to be the most primitive type
Zygote Fungi (Zygomycota):
The Molds, Mychorrhizeal, and Decomposing Fungi
Common black bread mold is a zygote fungi, and
all of the mycorrhizae are zygote fungi, or zygomycetes
(the suffix -mycete means "fungus".)
They all are composed only of hyphae, which gives
rise to another common name for this phylum: the
Threadlike Fungi. They are important decomposers
of dead organic matter, so this is a very important
group. They can reproduce either sexually or asexually.
Their cells may not have cell walls between the
cells (septa), so the nuclei can move along the
hyphae and it is hard to tell where one cell ends
and another begins. They are mostly terrestial
and live in soil or on decaying plant and animal
Common mold Rhizopus
destroying a tasty bunch of strawberries
Lets look at the mold on the strawberry a little closer,
so we can learn more about this common type of fungus.
This is a basket of strawberries
that is a few days old. It was not refrigerated.
Notice the wispy mold growing. This mold is called
Here is the mold growing on
one strawberry. The strawberry is soft and soggy,
due to the hyphae of the mold growing inside,
secreting digestive chemicals.
These are the sporangia, or
spore producing structures, part of the asexual
(Photos by D. Nelson, June 23,
2004. The closeup photograph was taken with a
digital camera, through a pair of binoculars,
but looking backwards.)
Sac Fungi (Ascomycetes):
Mildews, Yeasts, and Morels
Mildews and yeasts are part of the sac fungi,
as well as the morels, mushrooms that are very
highly prized for their flavor. They can cost
hundreds of dollars an ounce, so this group is
rather important, too. It is the largest group
of fungi, with over 60,000 described species (according
to Campbell's), and are found in a variety of
habitats, including marine, freshwater, and terrestrial.
They range in size from the single-celled yeasts
to the tasty morels.
The edible ascocarp of a sac fungi,
Club Fungi (Basidiomycetes):
This group, with about 25,000 species, contains
the mushrooms and the shelf fungi. The majority
of the fungus is underground, but when it needs
to reproduce, the fruiting body, called a basidiocarp
by scientists by called a mushroom by everyone
else, is formed.
The name comes from the Latin "basidium",
which means "little pedestal", obviously
referring to the mushroom shape.
For more information on mushroom, click here.
Fairy Rings are the fruiting bodies, or basidiocarps,
also known as mushrooms, that are being created
by an underground fungi. Another explanation is
that fairies were dancing around on a moonlit night
This shelf fungi was photographed a bit downstream
of Caz, along the road to CazSonoma Inn, June, 2004.
They are important decomposers of wood, which contains
a complex polymer called lignin, which few organisms
can digest. Without basidiomycetes, we would be
buried under piles of dead wood, and our forests
would not be able to grow, as all the nutrients
would be locked up in the dead wood.
My Foot Fungus Author
via Fungifama, So. Vancouver Island Myco. Soc., May
I'm growing fungus on my feet.
To tell the truth, it's kinda neat.
I grew it for my science class.
It's got so big, I'm bound to pass.
But it's not easy growing mold.
You must keep it dark and from the cold.
Put your socks on when they're wet,
And feed your fungus lots of sweat
It's been a month since I last showered,
And because of this, it's truly flowered.
It's amazing just how fast it grows.
You've never seen such fuzzy toes!
It has the most delightful hue.
It's sorta green and sorta blue.
But there are drawbacks to its fungal riches.
You won't believe how much it itches.
And the smell is gross, I have to say.
But it's worth it all to get an "A''.
The Natural Kingdom has a section on
University of Hawaii Introduction
to the Fungi.
Sidwell Friends School in Washington, DC, has an interesting
Volk, a professor of biology, has a great
The section on fungi is based almost entirely on the
excellent book Biology, by Campbell
and Reece. It is a college text for beginning biology
students. I cannot recommend it highly enough. If it
has been a few years (!) since you have had biology,
you will not believe how much things have changed. Not
only is there a lot more known about biology, the presentation
of the material is vastly improved. From text that is
closer to literature than dry explanation, to color
illustrations and color photographs that are so widely
used, I doubt that in its entire 1240 pages, there are
any without at least three or more color graphics of
some sort. And that does not even begin to explore the
enclosed CD or associated online material. I will eat
my hat if you don't love the book. I bought mine online,
This section is also based on my daughter Maggie's
seventh-grade biology book, Focus on Life Science, part
of the Prentice-Hall Science Explorer Series. It may
be hard to believe, but almost all of the material on
this page is seventh grade science! A lot has changed
since I was in seventh grade.
The photograph of mycorrhyzae was found at website
Anselm College, but appears to be from
Campbell's Biology, referenced above. The photograph
of the structure of a mushroom was from the website
for a software
company, efflare. The chytrid photo
is from Cal Poly. The top photo of
mold on the strawberries is taken from the University
of Alaska webpage on fungi, but seems to be
orginally from Campbell's Biology. The other photographs
of mold on strawberries, including the closeup, were
taken by D. Nelson. The morel is from Penn
State's webpage on fungi. The club fungi is from
University and Research Network website.
The fairy ring was from the Alabama Cooperative
Extension's website on agricultural pests.
*This webpage was originally created
while at 30,000 feet, flying from Paris to San Francisco,
June 18, 2004.