| What is a mushroom?
Mushrooms are the fruiting bodies of certain fungi---the equivalent of the apple, not of the tree. Fungi, including those which produce mushrooms, are not plants; they are related to molds, mildews, rusts, smuts, and yeasts, and are classified in the Fungi Kingdom.
The fungal organism which produces the mushrooms you encounter on your lawn or in the forest is called a mycelium. It is composed of hyphae, which are "chains" of fungal cells (singular: hypha).
The mycelium itself is typically hidden in a substrate---within dead wood, for example, or in the soil. There, hidden, it secretes enzymes to digest organic matter, and the hyphal cells absorb nutrients through their cell walls. Depending on the species and the circumstances, the mycelium may be quite small, contained for example within the hull of a single black walnut; or it may be remarkably huge---some cover many acres of forest floor.
If a mycelium thrives, eventually it will have enough energy to reproduce. When conditions are "just so"---a combination of day length, heat, humidity, and other factors---the mycelium will generate new hyphae which, within several weeks, will develop into the highly organized structure we call a mushroom. NOTE: not all fungi produce mushrooms; some reproduce asexually, at a microscopic level.
The slang term "toadstool" is best avoided, as it is ambiguous: to some people, "toadstool" implies a poisonous mushroom; to others, it means a mushroom with an umbrella-like shape.
Mushrooms take many physical forms or shapes in addition to the familiar umbrella-like "cap-and-stalk" structure most people picture when the word "mushroom" is mentioned. Some mushrooms look like balls; marine coral; cups or saucers; shelflike growths on trees, logs or stumps; sponges; bushes; or even cauliflower.
Here is the best definition of the term "mushroom" as applied by mycologists (those who study fungi), mycophiles (those who love fungi), mycophagists (those who eat fungi), and consumer books on mushrooms and other fungi:
MUSHROOM: a structure, produced by a fungus, that is large enough to be visible to the naked eye and has as its primary function the production of sexual reproductive spores.
Fungi rot dead things, right?
Yes, but that's just the tip of the fungal ecology iceberg!
Many fungi decompose dead organic matter such as leaves, wood, feces, etc. Many fungi are uniquely adapted to decomposing lignin---the hard "skeletal" tissue of wood. No other organisms can efficiently do this. But other fungi have other ecological roles, and few people know about the importance of that!
For example, many species of fungi are mycorrhizal (the term translates to "fungus-root"); rather than merely decomposing organic matter for a living, they have a vital symbiotic relationship with trees and other green plants. At least 90% of all land plants, including all trees, have mycorrhizal fungi! The plant "feeds" the fungus some of the carbohydrates it makes through photosynthesis; the fungus dramatically increases the tree's roots' absorption of water and certain essential minerals, such as phosphorus and magnesium, which the plants have poor access to without their fungal partner's help.
Without mycorrhizal fungi, most plants---including the grass on your lawn---would not survive and thrive! (That's why "chemical lawn services" will not apply fungicides to eliminate mushrooms for homeowners who don't like "toadstools" on their lawns---the chemicals would also kill the essential beneficial fungi.)
Other fungi have a different role: they infect and kill things---insects, trees, even people (sometimes, and especially those with weakened immune systems)---for a living. Fungi cause most diseases of insects, as well as many diseases of trees and other plants.
Some fungi have evolved to take advantage of multiple food sources. For example, the Oyster Mushrooms you can buy fresh at many grocery stores break down and digest cellulose, but they have also developed mechanisms for literally trapping and then eating tiny little "worms" called nematodes; this gives them access to extra nitrogen.
How do fungi reproduce?
The Easy Stuff
Instead of seeds, fungi produce spores. In the case of fungi which produce mushrooms, that's the sole purpose of the mushroom---it is a spore-producing structure. (Some fungi produce spores differently, without producing a visible structure that could be called a mushroom.)
The "body" of the fungus is called the mycelium. It is a tangled network of microscopically-thin filaments called hyphae, and it is typically hidden---in the humus on the forest floor, within decomposing wood, wrapped around the rootlets of a green plant, or wherever else serves as its dining room.
When conditions are right (humidity, day length, humidity, temperature, etc.) a fungus will produce new hyphae that are far more organized than those in the mycelium: a mushroom. This process takes longer than most people think---typically several weeks or more from the time the mushroom first starts forming until the time it is able to produce spores.
The More Technical Stuff
or you may... Skip it!
Most mushrooms are Basidiomycetes. Specialized cells called basidia (singular: basidium) produce the spores, which are more specifically called basidiospores, on tiny projections called sterigmata (singular: sterigma). (Some mushrooms---most notably the morels and related "cup mushrooms"---are Ascomycetes; they produce spores differently, within tube-like cells called asci (singular: ascus.)
If two basidiospores of the same species are lucky enough to germinate into primary or monokaryotic mycelia (each cell of which has one nucleus---see "A" and "B" in the illustration) in close proximity to each other, they can "mate" by forming a secondary mycelium with two nuclei per cell. This secondary or dikaryotic mycelium (see "C" in the illustration) is capable of eventually producing more mushrooms.
It is in the basidium that meiosis and keryogamy occur... in short, two nuclei become four---one for each of the four spores each basidium produces. (There are some exceptions to this, i.e. mushrooms whose basidia typically produce only two spores each.)
Do all mushrooms grow in the dark?
NO. Many mushrooms (for example, those sought-after springtime delicacies called morels) require direct sunlight. Little-known fact: several kinds of mushrooms GLOW in the dark!
How many kinds (species) of mushrooms are there?
It is estimated that there are at least 10,000 species in North America alone.
How many of them are edible?
About 250 North American species are known to be edible, and a similar number are known to be poisonous; the rest we're not sure about. NOTE: Most of the common, attractive mushrooms are known to be either edible or toxic.
How do you identify mushrooms?
Many species are very difficult to identify correctly, often requiring microscopic study and scientific books (and there are still plenty of species that haven't even been named yet!). On the other hand, many---including some wonderful edibles such as morels and puffballs---are rather easy to learn. Still, one MUST be careful. Identifying mushrooms requires you to study the specimens---size, color, odor, form of growth (in clusters or singly), habitat (growing on a pine log vs. growing on a lawn), and time of year are all important clues to a mushroom's identity.
The stalk must be examined very carefully---is there a ring of tissue (technically called an annulus) on the upper stalk? Is there a cup-like sac (a volva) around the very base of the stalk? (The latter is a feature of the often-fatal Death Cap (Amanita phalloides) and Destroying Angel (Amanita virosa) mushrooms.)
With most mushrooms, a very important character to consider is the spore print color. Though spores are microscopic, mushrooms produce millions of them. If you cut the stalk off a mushroom and place the cap right-side-up on a sheet of clear plastic (white paper can be used, but clear plastic is better for viewing a pale spore print) and cover it with a bowl and leave it overnight, it will usually deposit millions of spores, and you can see their color en masse.
Never "identify" a mushroom to eat by simply matching it to a picture! The specimen must be carefully compared to the description, including spore print color, etc.
A brief illustrated on-line treatise on the art of mushroom identification will soon be available for your perusal.
Is it dangerous to eat wild mushrooms?
How dangerous is it to drive a car? If you're drunk or careless, it is VERY dangerous; if you're sensible and pay attention, it is reasonably safe. Most mushroom hunters have never even gotten sick from eating wild mushrooms. It is a good principle for the novice to stick to the most easily identified edibles, such as morels, puffballs, and a few others.
Newspaper reports of serious mushroom poisonings often refer to the victims as "experienced mushroom hunters." But, as a rule, they don't even know what a spore print is; they just think they know what a certain edible mushroom looks like. Most victims of life-threatening mushroom poisoning in North America are people from Southeast Asia; they mistake Death Caps (Amanita phalloides) for edible "Paddy-Straw" (Volvariella volvacea) mushrooms. The two are similar in several ways---cap color, size, and the white "cup" around the base of the stalk---but different in others (for example, the Paddy-Straw has a pink spore print, the Death Cap a white spore print; and the Death Cap has a partial veil). The Paddy Straw mushroom occurs in tropical and temperate areas worldwide; the Death Cap, alas, does not occur in Southeast Asia, so folks from that part of the world are unaware of the lethal "look-alike."
An Important Note About Mushroom Names
Amateur mycologists soon learn that using "common" names for mushrooms is a tricky business, as each field guide seems to have its own set of "common" names. The least confusing "common" names for North American mushrooms are those presented by Gary Lincoff's Audubon Society Field Guide to North American Mushrooms and David Aurora's Mushrooms Demystified (for western North America).
To minimize confusion, amateur mycologists rely on the scientific names of mushrooms. At first, this may seem intimidating, but in reality the scientific names are no more difficult than some we all know: Tyrannosaurus, Rhinoceros, Hippopotamus.
An Important Note About Wild Hallucinogenic Mushrooms
While many mycologists will privately confess that they have had postitive experiences with hallucinogenic mushrooms, here is a word to the wise: Take it slow!
Contrary to popular opinion (at least in some circles), "bad trips" are as much a danger with Psilocybin and other psychoactive mushrooms as they are with LSD. A good percentage of mushroom poisoning cases involve victims who thought they were going to have good "recreational" or "spiritual" experiences but ended up either having "bad trips" or eating something dangerously toxic.
If you are committed to finding and eating hallucinogenic mushrooms, prepare to learn a lot first---or risk paying an exorbitant price for making a serious mistake!
An Important Note About "Kombucha"
First, Kombucha is not a mushroom; second; because of numerous reports of servious adverse effects, I do not recommend it to anyone. Read what mushroom cultivation expert Paul Stamets of Fungi Perfecti has to say about this odd and risky blob.
Interested in Cultivating Mushrooms?
No one knows mushroom cultivation better than Paul Stamets of Fungi Perfecti.
The study of mushrooms and other fungi is a fascinating area for amateur naturalists. There are three ways to learn more, and combining the three is the best way to learn:
Mycological Societies (Mushroom Clubs)
There are many mushroom field guides available for North America; the following are some of the most popular ones.
The Audubon Society Field Guide to North American Mushrooms by Gary H. Lincoff (Knopf; 1981). A handy, portable book with more than 700 full-color photographs.
A Field Guide to Mushrooms of North America (Vol. 34 of the Peterson Field Guide Series), by Kent H. and Vera B. McKnight (Houghton-Mifflin; 1987). Also portable, with more than 700 paintings and drawings of mushrooms. NOTE: the "common" names used in this book are mostly anything but "common;" also, the numerous warnings ("do not eat/taste any wild mushroom without first obtaining an expert opinion...") are a bit much.
Mushrooms of North America by Roger Phillips (Little, Brown & Co.; 1991). A voluminous book with over 1,000 species illustrated, recommend only as a "supplementary" book because of the lack of thorough introductory info and keys.
Edible Wild Mushrooms of North America: A Field-to-Kitchen Guide by David W. Fischer and Alan E. Bessette (Univ. of Texas Press, 1992). The mushroom book specifically designed to answer the question, "Can I eat it?"
Mushrooms Demystified by David Arora ([second edition] Ten Speed Press; 1986). Written for the West Coast, this book nonetheless has extensive keys, including many species that occur elsewhere in North America. It also has more comprehensive general information than any other mushroom book, including a wonderfully helpful guide to the meanings of mushrooms' scientific names.
All That the Rain Promises, and More . . . : A Hip Pocket Guide to Western Mushrooms by David Arora (Ten Speed Press, 1991). Both 'hip' and pocketable, this is a companion guide to Mushrooms Demystified.
Mushrooms of Northeastern North America by Alan E. Bessette, Arleen R. Bessette and David W. Fischer (1997, Syracuse Univ. Press). This five-pound book includes 642 color photos and keys to some 1,500 species. (For the purposes of this book, the "Northeast" is east of the Rockies and from Tennessee and North Carolina northward.)
Simon & Schuster's Guide to Mushrooms is not a good choice for use as a field guide in North America; it is a translation of an Italian work, hence is not a very useful identification manual for this continent. It is, however, a great general-interest mushroom book, with excellent introductory information.