A fungus is any member of a large group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms.
Fungi are a diverse kingdom, with members ranging from the familiar mushrooms to brewer's yeasts, the mould that grows on rotting fruit and the infection that causes athlete's foot. Fungi are found in every habitat, although they play a bigger role in terrestrial ecosystems than in aquatic ones. The vast majority of plants have a symbiotic relationship with fungal species that grow on their roots.
It is estimated that there may be anything from 700,000 to 5 million species of fungi in the world. Even using the most widely cited estimate of 1.5 million, this makes fungi more than six times as diverse as flowering plants. Yet only about 100,000 species have so far been described.
Fungi appear like plants but are closely related to animals. Fungi are not capable of producing their own food,so they get their nourishment from other sources. Fungi are in a wide variety of sizes and forms and have great economic importance.