Parasitic fungi species that parasitise and kill both trees and shrubs have more serious consequences for gardeners and park keepers. One such toadstool is honey fungus, which in older books went under the name Armillaria mellea and whose destructive nature is outlined in Chapter Twenty-two. Lawns are home to many species known as ‘little brown jobs’, of which brown mottlegill or hay cap (Panaeolina foenisecii) is the most common. This poisonous toadstool is not infrequently devoured by inquisitive young children and also by dogs, but the outcome is rarely serious, if worrying for parents and pet owners. I was pleased to find magic mushroom (Psilocybe semilanceata) growing on my own back lawn (see here), but lawn fanatics, along with bowling and golf green keepers are less enamoured of fairy ring fungus (Marasmius oreades), which often disfigures the turf on which it grows (see here).
As the organic, recycling movement has spread so the garden compost heap has made a comeback. Microfungi and bacteria are responsible for the breakdown of organic waste, a process that may cause the compost to reach temperatures as high as 60°C. Such conditions are only tolerated by thermophilic (heat-loving) toadstools including some species of inkcap (Coprinus spp.). Older heaps are occasionally colonised by wood blewit (Lepista nuda), whose mauve-gilled fruitbodies are edible and excellent; a bonus for the organic gardener. The use of woodchip on paths and as a garden mulch has ‘mushroomed’ in the past 20 years, bringing with it a range of toadstools not previously encountered in gardens or anywhere else in Britain (see here). Equally, the growing of exotic plants in heated greenhouses and conservatories has resulted in increased sightings of tropical fungi in Britain. Among the most conspicuous of these is plantpot dapperling or yellow parasol (Leucocoprinus birnbaumii), a bell-shaped little toadstool recognised by its bright yellow, scurfy cap with a distinctly grooved margin. Its first European record, in the early part of the 19th century, was in Prague Botanic Garden.
Another relatively new habitat has provided a novel home for a previously unusual British fungus. This is the very beautiful split-gill (Schizophyllum commune). Looking like a small furry bracket fungus from above, the underside reveals a fan-like, coralloid mass of branching gills. Most British records up until the middle of the 20th century came from south-eastern England, where it grows on fallen wood (especially beech) exposed to the sun. By the start of the 21st century I had begun to find it in the Peak District, possibly an example of a move northwards under the influence of climate change. As a thermophilic species it is more common in tropical regions, but it has now found a new home in Britain; plastic-wrapped bales of hay. The mycelium grows on the warm contents of the bags and its fruitbodies emerge through the plastic lining.
Wood blewit– Lepista nuda
{Laurie Campbell/NHPA}
In 2002 the same fungus made headlines with its ability to grow in another warm place: the human body. ‘Fatal Fungus that Preys on Humans’ was the title for one newspaper story. The fungus mycelium has been found to cause mouth ulcers and toenail infections; hardly fatal, but the fungus can be much more of a problem for people suffering from a suppressed immune system, including those infected with HIV or anyone taking immunosuppressant drugs.
Given that, unlike green plants, mushrooms and toadstools do not require light for the maintenance of their nutrition, it should come as no surprise that caves and old mines have been, and still are, used to grow edible mushrooms. In France the ordinary white mushrooms are still known as Paris mushrooms from the time when they were only cultivated in old mines beneath Paris. A number of fungi occur naturally in such habitats, including some microfungi that are not found anywhere else. Of the larger fungi growing in old mines, some species attack wooden pit props, such as the mine fungus (Antrodia vaillantii), a bracket fungus that also rots wooden greenhouses and has even been recorded growing on wet coke. Dry rot (Serpula lacrymans) also occurs in mines, where it may assume unusual growth forms (see here).
A small number of toadstools obtain their food by growing on, or in close proximity with, the fruitbodies of other fungi. Parasitic bolete (Pseudoboletus parasiticus) is a small yellow-brown-capped bolete that is occasionally found growing from the base of fruitbodies of common earthball (Scleroderma citrinum). As its name implies, it has long been presumed to be parasitic on the earthball, but some researchers believe that it only requires the presence of the earthball to stimulate fruiting and is not a parasite. Similar doubts surround the rare piggyback rosegill (Volvariella surrecta), which I have only seen once in the past 30 years when I found clusters of the toadstool emerging from the decaying remains of some clouded agarics (Clitocybe nebularis). The rosegill could be a parasite or live only on the dead fruitbodies of clouded agaric; it has never been found in any other situation. The well-known yellow brain (Tremella mesenterica), a jelly fungus that brightens old stems of gorse and other shrubs through the winter, has now been found to be parasitic on the mycelium of another fungus within the twig. Life is not always what it seems.
Microfungi occupy many more habitats than do the larger mushrooms and toadstools. These include both fresh and salt water. British examples of the former that have come to public attention are fish moulds, one of which causes black patches and the untimely death of many a pet goldfish, and another which results in the death of salmon. Fungi also attack insects, including house flies, and the honeycomb of hive bees. Plant parasites include the rust fungi which, along with mildews and related ‘moulds’, cause immense damage in both horticulture and agriculture. Microfungi cause food spoilage and also kill trees, although the fungus that has left its mark by killing elm trees is in fact an ascomycete, but with tiny fruitbodies that are rarely seen (see here).
Bread mould–Rhizopus stolonifera, scanning electron micrograph of a sporangium
{Jeremy Burgess/NHPA}
Humans provide an unwelcome home for fungi in the form of ringworm and thrush. Some fungi have even caused eye infections in contact lens solutions. Species of Malassezia, tiny yeast-like fungi, are present on our skin where they feed on the oily products of our sebaceous glands. These fungi can cause dermatitis and more commonly the shedding of skin flakes; so even dandruff can be blamed on fungi. Other microfungi result in the brown foxing seen in old books, the etching of the glass in cameras and field glasses, and the spoiling of the surface of CDs.
Perhaps most intriguing of all is the fungus that ‘eats’ jet and diesel fuel. Oil is, of course, an organic material, being composed of the long-dead remains of marine organisms, so it should come as no surprise that a range of microfungi has been detected in oil-based fuels. The most important of these is the creosote fungus Amorphotheca resinae, which not only breaks down creosote (which has been used as a preservative against fungi) but can also feed on jet fuel (kerosene) as long as at least a little water (ten parts of water per million of fuel is enough) is available. Empty tanks are vulnerable to condensation in humid conditions and this can provide the necessary water. High-flying aircraft experience very low temperatures, but the creosote fungus can put up with temperatures down to –25°C. The greatest danger to planes and their passengers comes from the fungal mycelium, which may block filters and small pipes, thus preventing fuel flow to an engine.
As with all fungi, preventing the initial infection is one way of limiting damage. Many years ago I was told a story by someone who had worked for the RAF. He recounted a big NATO exercise involving jet planes from different countries which, as part of the training, were refuelled in mid-air from special tanker planes. Only later was it discovered that one tanker plane was infected with creosote fungus and,