Mushrooms are the spore-bearing structures of fungi, a kingdom of organisms that get energy mainly by decomposing dead and sometimes living plant and animal material. It is estimated that the top 20 centimeters (nearly 8 inches) of fertile soil may contain nearly 5 metric tons (5.5 tons) of fungi and bacteria per hectare (2.47 acres). Some 100,000 species of fungi have been described; scientists estimate that as many as 200,000 more await discovery. Fungi are the single most important cause of plant diseases and some fungi cause serious diseases in people and animals. However, associations between fungi and plant roots called mycorrhizae are in about four-fifths of all land plants; these associations are critical in supplying certain nutrients to plants. In addition, some kinds of fungi, like yeast and penicillin, have proven extremely useful to humans. Of course, mushrooms are also valued as food and certain species are considered delicacies. Many species of mushrooms in Missouri are edible, but proper identification is essential to avoid illness and even death by toxic mushrooms. (text courtesy Missouri Department of Conservation.)