Out of damp and gloomy days, out of solitude, out of loveless words directed at us, conclusions grow up in us like fungus: one morning they are there, we know not how, and they gaze upon us, morose and gray. Woe to the thinker who is not the gardener but only the soil of the plants that grow in him. ~ German philosopher Friedrich Nietzsche
Fungi are a diverse group of eukaryotes with a complex classification, as there are well over a million species. Fungi fall into 2 general sizes: microscopic and macroscopic.
Fungi differ from all other life. Unlike plants and animals they form no embryos. They grow from tiny propagules, packages called spores. ~ Lynn Margulis
Fungi can be mighty hardy: thriving in harsh habitats as well as more hospitable conditions. Fungi keep their cool in deserts, savor salty settlements, not agonize over ionizing radiation, and sink without being down in deep-sea sediments. Some fungi are astronaut-ready: able to survive the intense UV and cosmic radiation encountered during space travel.
Most fungi, though, are much more down to Earth. Fungi are among the most prolific soil microbes. Topsoil averages over 8.2 tonnes of fungal mycelia per acre.
A mycelium is an integrated organism. Mycelial cords can transfer nutrients over long distances. This lets a fungus grow through soil from an established food store in search of a new supply.
Fungi are like plants in some ways but cannot produce their own food through photosynthesis. Instead, they gain nourishment by breaking down organic matter.
Most fungi are saprovores, but fungal parasites do not wait until the food is dead. They sate themselves by gnawing on the living.
Fungi are important recyclers in every ecosystem. They break down the departed, thereby burying the dead to feed the living. What fungi don’t absorb are essential nutrients that are recycled into the soil for uptake by microbes and plants.
Major fungal groups differ in reproduction, both by sexuality (asexual, sexual, or alternatively both), and by the way they produce spores. The degree of sexual diversity may seem somewhat surprising, in that all fungi evolved from a common ancestor. But sexuality is simply an adaptable life-history variable, as flexible as any other trait from an evolutionary perspective.
Fungi clearly are intelligent, even as they lack any physiology for it.
In both plants and animals, electrical and chemical signaling is known. It’s not clear what happens in a fungus. Yet multicellular fungi coordinate the distribution of nutrients and their behavioral responses. ~ Swiss microbiologist Markus Künzler
Fungi recognize each other and are territorial. If the mycelium of an individual fungus splits into smaller networks, they happily grow independently. If they later encounter one another, they may fuse back together to form a more robust mycelium by pooling resources.
If a fungus encounters a conspecific, they build chemical fences that mark territorial boundaries. In contrast, when interspecific fungi meet, war often breaks out. Each fungus produces various agents to terminate with extreme prejudice. Concoctions may be adjusted to improve toxicity. Their genome offers a variety of lethal cocktails which a fungus may choose from, as well as providing inspiration for brewing innovations.
Fungal fighters think strategically. Beset by enemies on different borders, a fungus will pick off the weakest enemy first, so as to consolidate resources for taking on stronger opponents. Bystanders may affect the outcomes of battles by emitting some of their chemical arsenals, or staging skirmishes to weaken a dominant contender.
Fungi associate with a wide variety of other organisms, often as mutualists. Their friendly relations with plants are legion. Other fungi are not so benevolent, existing as parasites and pathogens on or in plants, animals, and other fungi.