The term mushroom is not a taxonomic division. Mushrooms are microfungi with distinctive fruiting body. which can be hypogeous or epigeous, large enough to be seen with the naked eyes and to be picked by hand (Chang and Miles,1992). They include both edible/medicinal and poisonous species. However, originally, the word “mushroom” was used for the edible members of macrofungi and “toadstools” for poisonous ones of the “gill” macrofungi. Scientifically the term “toadstool” has no meaning at all and it has been proposed that the term is dropped altogether in order to avoid confusion and the terms edible, medicinal and poisonous mushrooms are used.
Edible mushrooms once called the “food of the gods” are nutritionally endowed fungi mostly basidomycetes which grow naturally on the trunks ,leaves and roots of decaying woody materials(Stamets 2000).Edibility of of mushroom maybe defined by criteria that include absence of poisonous effect on human and desirable taste and aroma
Since mushrooms lack chlorophyll they can not, like green plants, get their energy from the sun through photosynthesis. Instead, during their vegetative growth stage, mushroom mycelia secrete enzymes that break down compounds such as cellulose and lignin present in the substrate. The degraded compounds are then absorbed by the hyphae and the mycelium enlarges-usually laterally, and in some cases growing several meters in diameter with the substrate.
Partially understood environmental factors (temperature and light are known to be critical) stimulate the second or reproductive growth stage. Cells of one mycelial strain fuse with cells of the opposite type to form a mycelium that contains both types of nuclei. The new mycelium continues to grow and eventually develops into a mature fruiting body, the gills of which are lined with spore bearing cells called basidia. Various mechanisms trigger the dispersal of spores, which in turn lodge in a substrate, become hyphae and begin the cycle anew