Fungus (plural Fungi)

A fungus (plural fungi) is a eukaryotic organism that digests its food externally and absorbs the nutrient molecules into its cells. Fungi are used extensively by humans: yeasts are responsible for fermentation of beer and bread, and mushroom farming is a large industry in many countries. Fungi are the primary decomposers of dead plant and animal matter in many ecosystems, and are commonly seen on old bread as mold. However, the complex biology of fungi extends beyond this common knowledge and experience of them.

Phylogeny of Fungi

Originally classified as plants, fungi are not at all plants, because they are heterotrophs (they do not fix their own carbon through photosynthesis but use the carbon fixed by other organisms). Indeed, fungi are now thought to be more closely related to animals than to plants, and are placed together with animals in the monophyletic group of opisthokonts. However, unlike animals, fungi absorb their food rather than ingest it, and their cells have cell walls surrounding them. For these reasons, these organisms are placed in their own kingdom, Fungi.

The Fungi are a monophyletic group, meaning all varieties of fungi come from a common ancestor. Mycologists (scientists who study fungi) believe they are monophyletic because they have chitin in their cell walls and are absorbtive heterotrophs, along with other shared characteristics.

Overview

Although often inconspicuous, fungi occur in every environment on earth and play very important roles in most ecosystems. Many fungi are major decomposers of dead plant and animal matter in forests and many other environments. Some fungi are predators of nematodes, which they capture using an array of devices such as constricting rings or adhesive nets. Other types are parasites on plants and animals, including humans. They are responsible for numerous diseases, such as athletes foot and ringworm in humans and Dutch elm disease in plants. Other fungi are partners in symbiotic relationships with other organisms. For example, lichens are formed by a symbiotic relationship between algae or cyanobacteria and fungi. Most vascular plants benefit from a symbiosis between their roots and fungi.

Fungi have a long history of use by humans. Many types of mushrooms and other fungi are eaten, including button mushrooms, shiitake mushrooms, and oyster mushrooms. Of course, many species of mushrooms are poisonous and are responsible for numerous cases of sickness and death every year. A type of fungus called yeast is used in baking bread and fermenting alcoholic beverages. Fungi are also used to produce industrial chemicals like lactic acid, and even to make stonewashed jeans. Some types of fungi are ingested for their psychedelic properties, both recreationally and religiously.