fungus

fungus

Bracket fungus (Polyporus) growing on wood.

(credit: H.S. Knighton)

Any of about 200,000 species of organisms belonging to the kingdom Fungi, or Mycota, including yeasts, rusts, smuts, molds, mushrooms, and mildews. Though formerly classified as plants, they lack chlorophyll and the organized plant structures of stems, roots, and leaves. Fungi contribute to the disintegration of organic matter resulting in the release of carbon, oxygen, nitrogen, and phosphorus from dead plants and animals into the soil or the atmosphere. Fungi can be found in the water, soil, air, plants, and animals of all regions of the world that have sufficient moisture to enable them to grow. Essential to many food and industrial processes, fungi are also used in the production of enzymes, organic acids, vitamins, and antibiotics. They also can destroy crops, cause such diseases as athlete's foot and ringworm, and ruin clothing and food with mildew and rot. The thallus, or body, of a typical fungus consists of a mycelium through which cytoplasm flows. The mycelium generally reproduces by forming spores, either directly or in special fruiting bodies that are generally the visible part of the fungus. The soil provides an ideal habitat for many species. Lacking chlorophyll, fungi are unable to carry out photosynthesis and must obtain their carbohydrates by secreting enzymes onto the surface on which they are growing to digest the food, which they absorb through the mycelium. Saprophytic fungi live off dead organisms and are partly responsible for the decomposition of organic matter. Parasitic fungi invade living organisms, often causing disease and death (see parasitism). Fungi establish symbiotic relationships with algae (forming lichens), plants (forming mycorrhizae; see mycorrhiza), and certain insects.