It is neither a vegetable nor a fruit, nor a kind of meat, but it has been prized as food since ancient times. Mushrooms occupy a class all their own. They are fungi and are considered by many vegetarians as not quite belonging to the plant kingdom! Mushrooms have however, been eaten by people since ancient times, especially in China, Greece and Italy. The edible part of the mushroom is the fruiting body that grows on a stalk and has a cap and gills on the underside. There are 38,000 different varieties of mushroom, of which 1,841 are edible. Some species are mildly poisonous which is why eating wild mushrooms is not advisable. The outrageously expensive truffle is also a species of edible fungus that grows under the ground near the roots of old oak trees. The most popular variety of edible mushrooms, Portobello, are known as button mushrooms when they are young and unopened. Button mushrooms are available fresh, frozen or canned. They have a mild flavour if eaten raw, but are better cooked.