the fungus kingdom consisting of some 2.2 million to 3.8 million species is separated from plant, bacteria, protozoa and animal kingdoms by the presence of chitin-glucan complexes in their cell walls
fungi are the principal decomposers in ecological systems and have fundamental roles in nutrient cycling and exchange in the environment
most fungal structures are microscopic but they may become visibly noticeable when fruiting, either as mushrooms or as molds
many species produce bioactive compounds called mycotoxins, such as alkaloids and polyketides, that are toxic to animals, including humans such as:
lethal amatoxins in some Amanita mushrooms
ergot alkaloids, which have a long history of causing serious epidemics of ergotism (St Anthony's Fire) in people consuming rye or related cereals contaminated with sclerotia of the ergot fungus,
Claviceps purpurea
aflatoxins, which are insidious liver toxins and highly carcinogenic metabolites produced by certain Aspergillus species often growing in or on grains and nuts consumed by humans
ochratoxins
patulin
trichothecenes (e.g., T-2 mycotoxin)
fumonisins
psychedelic “magic mushrooms”
certain fungi, in particular white-rot fungi, can even degrade insecticides, herbicides, pentachlorophenol, creosote, coal tars, and heavy fuels and turn them into carbon dioxide, water, and basic elements
DNA analysis suggests that all fungi are descended from a most recent common ancestor that lived at least 1.2 to 1.5 billion years ago
the earliest fossils possessing features typical of fungi date to the Paleoproterozoic era, some 2,400 million years ago (Ma), the estimated age of the oldest terrestrial lichen fossil is 415 million years
lichens are a symbiotic relationship between fungi and photosynthetic algae or cyanobacteria
many insects actively cultivate fungi for mutual benefit
many fungi are parasites on plants, animals (including humans), and other fungi
some are carnivorous
fungi can be infected by other fungi, bacteria or mycoviruses