Introduction

The Fungus Kingdom
Neither plants nor animals, fungi constitute what specialists call Mycota, or the fungus kingdom. On the tree of life, fungi are closer to animals than to plants. Indeed, fungi have many traits in common with animals, including the inability to perform photosynthesis, because they lack chlorophyll in their cells. Fungi must therefore obtain the organic material that they need to grow from other organisms; in scientific terms, they are heterotrophic. Another trait that fungi share with animals is that they store carbohydrates in the form of glycogen, whereas plants do so in the form of starch. Fungi even produce chitin, a nitrogen-containing substance that forms their cell walls and that is also found in the exoskeletons of insects.

The fungus kingdom includes all organisms that meet the following criteria. They must have a nucleus in each cell (which defines them as eukaryotes), cell walls made of chitin, and a vegetative apparatus (mycelium) composed of a network of microscopic filaments called hyphae. To be considered fungi, organisms must also reproduce by spores and be heterotrophic and absorbotrophic (digest their nutrients outside their cells, then absorb them in the form of small molecules through their cell walls).

Although the number of fungus species is not known, fungi are probably the most numerous living organisms after insects. About 100,000 species of fungi have been described so far worldwide, but the total number in existence is estimated at 1 to 1.5 million. Many new species are being discovered every year, and the task of inventorying them all is far from over.

An Ancient Realm
Very little is known about the origins of fungi, and fossil fungi are unfortunately extremely scarce. Some rare specimens have been found preserved in amber, including a Coprinites dominicana (an extinct species closely related to the genus Coprinus) discovered in the Dominican Republic and dated at over 15 million years old. The oldest mushroom fossils ever found date back more than 400 million years, to the Devonian period, when the first terrestrial vertebrates appeared. Among these fossils are some Chytridiomycota -- also known as chytrids -- the most primitive fungi still living on Earth. The chytrids are microscopic species. They are mostly aquatic, and their spores have the distinctive feature of a flagellum that gives them mobility.

What Are Mushrooms?
But what exactly are mushrooms? Like a plant, a fungus consists of a vegetative portion and a reproductive portion. In fungi, the vegetative portion is the mycelium, and the reproductive portion is the sporophore. This sporophore is what we usually call a "mushroom". In this book, we will be talking only about macroscopic fungi: those whose sporophore is visible to the naked eye.

The mycelium of a fungus usually grows underground, and it grows constantly, to a considerable size and age. The world record is currently held by an Armillaria ostoyae in Oregon, in the United States. This living fungus is over 2,400 years old. Its mycelium weighs around 661 tons (600 tonnes) and covers an area of nearly 3.5 square miles (9 square kilometers)!

In contrast, the sporophore of a fungus lives a much shorter time: scarcely a few hours, in the case of certain coprinoid fungi; sometimes just a few day; and a few years at most for certain polypores, such as the tinder fungus. The sporophore is usually aerial, but in some species, such as truffles, it grows underground. In some cases it is tiny, measuring a few thousandths of an inch at most, but in others, it can reach impressive dimensions. For example, the Giant Puffball can weigh over 22 pounds (10 kg) and exceed 27 inches (70 cm). Mushrooms vary tremendously in appearance, which is why it is always so exciting and amazing to see them grow.

Feeding and Reproducing
Fungi feed in three different ways. One large group of fungi, known as saprophytes, feed on decomposing organic matter. A smaller group, parasitic fungi, feed on other living organisms. The third group comprises numerous fungi that maintain symbiotic relationships with other living organisms: either plants or animals. (Fungi that live in symbiosis with vascular plants are known as mycorrhizal fungi.)

The sole function of the sporophore (the mushroom) is to produce and spread spores, which then germinate and develop into a new, primary mycelium. But whereas in plants, a single seed develops into an entire new plant, in fungi, two primary mycelia must merge to create a secondary mycelium, and only the secondary mycelium can produce new sporophores. Note, however, that some fungi can also propagate vegetatively, a form of asexual reproduction that results in the birth of clones.

Mushrooms and Humankind
People use mushrooms in many different ways. The most widespread use, of course, is as food. Mushrooms were a prized delicacy in Ancient Rome and were first cultivated in Asia over 900 years ago. Nowadays, hundreds of thousands of mushroom lovers go hunting for them in the fall, even though many mushroom species can be poisonous or even fatal to eat.

Mushrooms can also have medicinal properties, as was already known in prehistoric times - for example, traces of three species of medicinal mushrooms were found in the equipment of Ötzi the Iceman, the Neolithic hunter whose naturally mummified body was found frozen in the ice in the Austro-Italian Alps in 1991. Today, more and more research is being done on the medicinal properties of mushrooms, with some promising results.

The use of mushrooms for ritual, spiritual and religious purposes also dates back to the dawn of time. Even now, shamans in some cultures still use hallucinogenic mushrooms, which the Aztecs worshipped as the "flesh of the gods", to enter into the invisible world.

But you don't need to eat magic mushrooms to share in the magic of the mushroom world. In their effort to produce as many spores as possible and spread them as effectively as possible, mushrooms grow in such a variety of sizes, shapes and colors, and have so many different smells and textures, that you can experience their magic with your ordinary senses alone. Simply go outside and walk around with your eyes open for mushrooms large and small. We hope that the beautiful photographs on the following pages will inspire you to do just that!