fungus

Fungi grow from spores as fine threads, or hyphae. These have no distinct cellular structure. Mushrooms and toadstools are the fruiting bodies formed by the hyphae. Gills beneath the caps of these aerial structures produce masses of spores.

Field, or meadow mushroom (Agaricus campestris). The edible field mushroom is one of about 60 species of Agaricus, a genus of gill fungi. The gills on the underside of the cap or pileus, contain the reproductive spore-bearing cells. Unlike plants, mushrooms (which are classified as part of the fungi kingdom) are not photosynthetic, but absorb food from the organic matter they live on or within. Agaricus bisporus, a close relative of the field mushroom, is the most widely commercially-cultivated mushroom.

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).

The oldest surviving fungi were found 1994 as dormant spores in the hay lining the boots of a hunter who died 5,300 years ago, and whose body was preserved frozen in the Alps. When the hay was placed on agar, fruiting bodies began to appear. Two species were present, Absidia corymbifera and Chaetomium globosum.

In 1992 an individual honey fungus (Armallaria ostoyae) was identified as the world's largest living thing, having an underground network of hyphae covering 600 hectares/1,480 acres. It was found in Washington State, USA, and estimated to be between 500 and 1,000 years old.

In 1996 Canadian researchers identified the protein collagen in the yeastlike fungus Microbotryum violaceum. It is the first time collagen has been identified in a non-animal source, and may provide evidence for a link between fungi and animals.