WHAT ARE MUSHROOMS ?

Historically, mushrooms were classified among the so-called lower plants in the Division Thallophyta by Linnaeus. This was largely due to the relatively simple, anatomically uncomplicated structural attributes (lack of true roots, true stems, true leaves, true flowers, and true seeds). The presence of a cell wall related them to plants rather than to animals. Modern studies have established that mushroom biota, together with other fungi, have features of their own, which are sufficiently and significantly distinct to place them in a separate fungal kingdom, the Kingdom Myceteae. The fungi differ from the plant and animal kingdoms by their possession of a cell wall that is different in composition from that of plants and a mode of nutrition that is heterotrophic but, unlike animals, is absorptive (osmotrophic) rather than digestive.

A. DEFINITION

The word mushroom has been used in a variety of ways at different times and in different countries. A broad use of the term mushroom embraces all larger fungi, or all fungi with stalks and caps, or all large fleshy fungi. A more restricted use includes just those larger fungi that are edible and/or of medicinal value. The most extreme use of the term mushroom is its reference to just the edible species of Agaricus

In this book the term mushroom is broadly defined as follows: “a mushroom is a macrofungus with a distinctive fruiting body which can be either epigeous (above ground) or hypogeous (under ground) and large enough to be seen with the naked eye and to be picked by hand.”

According to this definition, mushrooms need not be Basidiomycetes, nor aerial, nor fleshy, nor edible. Mushrooms can be Ascomycetes, grow underground, have a nonfleshy texture, and need not be edible. We believe that this definition has merit in establishing uniformity of terminology at a time when the number of cultivated species is increasing, when production of established cultivated mushrooms continues to show a steady expansion, and when an increasing number of countries and people are engaged in mushroom cultivation as an agricultural or industrial technology.

B. CHARACTERISTICS OF MUSHROOMS

The most common type of mushroom is umbrella shaped with pileus (cap) and stipe (stem), e.g.,

Lentinula edodes

(Figure 1.2), and some species additionally have an annulus (ring), e.g.,

Agaricus

bisporus

(Figure 1.3), or a volva (cup), e.g.,

Volvariella volvacea

(Figure 1.4)

,

or have both, e.g.,

Amanita phalloides

(Figure 1.5). Additionally, some mushrooms are in the form of pliable cups,

and others are round like golf balls. Some are in the shape of small clubs; some resemble coral;

others are yellow or orange jellylike globs; and some even resemble the human ear. In fact, there

is a countless variety of forms. The structure that we call a mushroom is in reality only the fruiting

body of the fungus. The vegetative part of the fungus, called the mycelium, comprises a system of

branching threads and cordlike strands that branch out through the soil, compost, wood log or other

lignocellulosic material on which the fungus is growing. After a period of growth, and under

favorable conditions, the established (matured) mycelium produces the fruiting structure, which

we call the mushroom.