The Fungi are a large group of organisms which are ubiquitous in terrestrial habitats. They are less abundant in freshwater habitats and comparatively rare in in the sea. Fungi are characterised by a filamentous growth form (mycelium), reproduction by haploid spores, and a sexual cycle which involves delayed nuclear fusion (dikaryon). A few groups form large sporulating colonies (mushrooms, toadstools, brackets etc).
Although usually thought of as decomposers, many have other lifestyles. Some are parasitic; a small number of these are of medical importance, but most are plant parasites and a few are economically very significant.
Other fungi form symbiotic relationships with plant roots (mycorrhiza). The fungus mycelium is able to permeate the soil further afield than the plant's root hairs and so can harvest minerals from a larger soil volume. These are made available to the plant while sugars from photosynthesis leak from the roots to the fungus. Many of the most striking autumn toadstools (Amanita, Cortinarius, Tricholoma, Boletus sl.) are mycorrhizal with forest trees (esp Oak, Beech, Hazel, Willow, Birch and Pine). Most other plants and trees are mycorrhizal with lower fungi like the Pea Truffles (Endogone). The exception is the Cabbage family, Brassicaceae, which is not known to form mycorrhizal associations and is rarely affected by Rust Fungi (the exception to the exception is Scurvy Grass - Cochlearia spp.) - this is probably due to the mustard oils which give them their distinctive flavour and smell.
Mycorrhizal fungi can be parasitised by higher plants, maybe with another fungus as intermediary. The plants formerly called "Saprophytes" fall into this category: there is insufficient nitrogen or useable carbohydrate in leaf litter to support a flowering plant.
Lichens are another example of fungi forming symbioses with photosynthetic organisms, in this case: algae or cyanobacteria. The combined organism is able to live in much harsher environments than either could alone. Some lichens grow just inside rocks (endolithic) where they wait for erosion processes to release their spores.
Prof D.L. Hawksworth has estimated that there are 6 species of fungus for every species of flowering plant, suggesting there are 1.5 million species of fungi on Earth. Less than 20% of these are known to science, although in Europe, which has been well-studied, the percentage is far greater.
Fungal specimens are best preserved by drying.
Infected plant material can be lightly pressed, although if there is superficial growth, this will be damaged and may be lost. Most people use gentle warmth for everything from leaf-spots to fleshy toadstools.
This can be as simple as the top of a radiator, although purpose-built driers such as those sold for drying fruit give the best results. Large fleshy species can be placed in the air stream from a fan heater for fast, effective results even with fragile species like inkcaps.
Infected leaves can be placed in folded blotting paper, lightly weighted on top to prevent them curling up too much.
The time taken to dry varies with the method, but can be from a few hours for infected leaves, overnight for small to medium toadstools, or longer for large toadstools or brackets. Large toadstools can become sealed by a dry layer on the outside, but leaving them at room temperature for a day allows the remaining moisture to soften this skin so drying can be resumed.
Leaves will curl and go crisp otherwise weight is the easiest way to tell when a specimen is dry. At this point it's best to leave them at room temperature for a day to soften up, otherwise they can be very fragile.
Dried material keeps reasonably well but is attacked by a variety of pests, especially booklice and mites, and to a lesser extent museum/carpet beetles. Dried material is conventionally stored in paper envelopes, but this gives no protection from insects, so the envelopes need to be stored in batches in sealable plastic bags or boxes. Avoid storing the specimens directly in individual plastic bags as static electricity from handling the bags will make extracting the dried material all but impossible.
Except for some of the more distinctive larger species, microscopic examination is always required to identify fungi. Staining is often necessary to make hyaline tissues and spores visible - the question is what stain to use? As a rule of thumb: if it has basidia, use Phloxine; if it has asci, use Melzer's Iodine; other hyaline ascomycete structures can be stained with Congo Red. Anamorphic fungi generally stain well in Cotton Blue, although dematiaceous hyphomycetes generally need no staining.
True fungi, including mushrooms, toadstools, cup fungi, moulds and lichens, but excluding those groups which used to be regarded as fungi until modern research showed them to be closer to algae (oomycetes) or protozoa (slime moulds).