fungus

Any of a unique group of organisms that includes moulds, yeasts, rusts, smuts, mildews, mushrooms, and toadstools. There are around 70,000 species of fungi known to science, although there may be as many as 1.5 million actually in existence. They are not considered to be plants for three main reasons: they have no leaves or roots; they contain no chlorophyll (green colouring) and are therefore unable to make their own food by photosynthesis; and they reproduce by spores. Some fungi are edible but many are highly poisonous; they often cause damage and sometimes disease to the organic matter on which they live and feed, but some fungi are exploited in the production of food and drink (for example, yeasts in baking and brewing) and in medicine (for example, penicillin).

Fungi are either parasites, existing on living plants or animals, or saprotrophs, living on dead matter. Many of the most serious plant diseases are caused by fungi, and several fungi attack humans and animals. Athlete's foot, thrush, and ringworm are fungal diseases. Endophytes are fungi that live inside plants. Almost all plants have endophytes and many have large numbers, for example the grass fescue has 400 species.

Before the classification Fungi came into use, they were included within the division Thallophyta, along with algae and bacteria. Two familiar fungi are bread mould, which illustrates the typical many-branched body (mycelium) of the organism, made up of threadlike chains of cells called hyphae; and mushrooms, which are the sexually reproductive fruiting bodies of an underground mycelium.

The mycelium of a true fungus is made up of many intertwined hyphae. When the fungus is ready to reproduce, the hyphae become closely packed into a solid mass called the fruiting body, which is usually small and inconspicuous but can be very large; mushrooms, toadstools, and bracket fungi are all examples of large fruiting bodies. These carry and distribute the spores. Most species of fungi reproduce both asexually (on their own) and sexually (involving male and female parents).