Fungi are a unique kingdom in nature that basically recycle all the organic crap that's made by plants and animals; that's why they're also known as "decomposers". They can be found in caves because unlike plants, they don't need sun to exist.
Despite having many apparently "plant like" features fungi are consumers as noted above - they break complex organic matter down into less complex forms1. As saprophytes they are sometimes referred to as "terminal consumers" in that they come somewhere near the end of the trophic chain.
The 'mushroom' part of the fungus is actually a very small part of the whole - merely the fruiting body for a much larger organism. The whole thing consists of a network (mycelium) of fibres (hyphae) which grow throughout the structure of whatever it is that it is feeding on: a "free standing" mycelium can be found in the form of the "fur" that grows in your kitchen bin when you forget to empty it. Fungi grow by the extension and division of the hyphae but reproduce by spores - airborne or waterborne particles with the potential to grow into new hyphae.
Besides their natural role in breaking down organic waste, fungi also have a variety of other uses:
- As food: fungi are a high fibre2, high protein, low fat and low salt food that contains few calories … not great on their own, but a good dietary supplement. In modern times, industrially grown fungal mass (e.g. Quorn) is increasingly marketed as an alternative to meat.
- As sources of chemicals: most natural antibiotics (e.g.. penicillin) are produced by molds, which are basically the same thing and fungi also produce several potent poisons and psychoactive substances such as psilocybin (the active in 'magic mushrooms') and muscarine (found in amantias like the fly agaric - used extensively in Shamanism). Ergot, a fungus that grows on spoilt grain, produces alkaloids which as well as being psychoactive and chemical precursors to LSD and the like, are also potent vasoconstrictors and useful in treating migraine and post-partal bleeding. Other uses for fungi exist, both in folk medicine and, increasingly in modern pharmacology.
- Biotech uses: yeasts (basically fungi) are used in making bread, wine, beer and other fermented drinks, molds are used to flavour blue and green cheese and to brew soy. Chemicals such as citric acid are produced by fungal fermentation as are many industrial enzymes.
- Environmental control: infectious fungi are increasingly used for pest control, either by competing out other species that damage crops or by infecting and killing pest species and insects. There are also efforts underway to breed fungal strains that either selectively take up pollutants such as heavy metals from the environment (allowing them to be harvested and the pollutants removed) or which break down toxic organic compounds such as coal tars, creosotes and organic pesticides.
- Dyestuff: some fungi can be used for cloth dying (see reference below)
- Miscellaneous: some of the bracket fungi make excellent kindling for those trying to light a fire.
Fungi can also be a nuisance - they don't differentiate between your food and equipment and any other non living matter when they are breaking stuff down. When your rations grow fur or your clothes become mildewed, that's fungi at work as well.
They can also try to eat you - normally they'll be limited to causing skin infections (like athletes foot and veruccas) but they can also cause internal infections (e.g. thrush), which can become a lot more serious if the patient is immune compromised (e.g. due to HIV, immunosuppressants or a curse). It is also possible for fungal spores to lodge in the lung and grow there, causing a lung infection which is very hard to diagnose and treat effectively.
Fungi are often used as cave flora. In some fantasy games they can move, talk, and fight. In World of Warcraft's zone called Zangarmarsh, fungi reach the size of trees, and they are the main landscape.
List of Fungi
Game and Story Use
- Mushrooms are an obvious source of material for the character with herbalist, alchemist and/or potion brewing tendencies. The folk healer may use lots of them.
- The use of mushrooms in folk magic may mean that in an RPG setting they provide some bonus to magic practice.
- Vat grown fungus is another obvious foodstuff for sci-fi settings, and is much nicer than it sounds.
- Mushrooms are the sort of thing that is often turned up on a successful foraging roll (and can be dried for use in iron rations) … if the roll is botched then the forager has found some toxic mushrooms instead. These can be very toxic indeed, merely psychoactive and annoying or somewhere in-between.
- Getting a fungal infection may be the result of some kind of failed survival roll ("you didn't look after your feet, and now the skin is coming off…").
- Outbreaks of ergotism - ergot poisoning due to contaminated grain supplies - caused all sorts of chaos during the middle ages, characterised by mass outbreaks of a burning sensation in the limbs ("St Anthony's fire") resulting from the vasoconstriction, dissociative behaviour and hallucinations. Such things were often blamed on witchcraft or possession and are more likely in communities already troubled by hunger and other troubles (such as conflict and bad weather).