This hard woody fungus is one of the most conspicuous fungi in the Caledonian Forest, and forms an important habitat for many invertebrates.
Tinder fungus grows on trees throughout the temperate and boreal regions of the northern hemisphere, and is found in Europe, northern Asia and in North America. In the north of its range it occurs mostly on birch trees (Betula spp.), but in parts of Europe it is widespread on beech trees (Fagus sylvatica) and also grows on sycamore (Acer pseudoplatanus) and aspen (Populus tremula). In North America it is most common on birches, but also occurs on maples (Acer spp.), poplars (Populus spp.) and alders (Alnus spp.). It has been recorded from Pakistan, northern Iran and Turkey, where it grows on poplars (Populus spp.), while in northern Japan it grows on Japanese beech trees (Fagus crenata). Tinder fungus has also been found on the island of Dominica in the Caribbean.
Tinder fungus occurs in much of mainland Scotland, but is most abundant in the Highlands, because the birch trees (Betula pendular and Betula pubescens) that are its main host are so widespread there. It is absent from Orkney and the Outer Hebrides, but occurs on Mull and Skye, and has also been recorded on Colonsay. In Scotland it is rarely found on species other than birch, but occasionally is seen on beech (which is its main host in the south of England), alder and aspen.
Tinder fungus is a tough, woody inedible fungus in the Polyporaceae family. It is a bracket fungus, meaning that it grows out of the wood of standing or fallen dead trees, and is also known as the hoof fungus, because of the similarity of its fruiting body to a horse's hoof. It is usually dark grey in colour, although when it is wet it can appear to be black, and when it is old and dry it can be bleached to an off-white colour. Old specimens can also be partially or almost fully covered in moss, especially in the wetter western parts of the country.
The upper surface of the fungus consists of concentric semicircular ridges, which result from the annual growth that the fruit body puts on. Some individuals are flat and shelf-like, while others are much more three dimensional in their growth, giving them the similarity to hooves. In size, they range from young specimens that may be 5 cm. in width to large ones that can reach 45 cm. across. Although solitary specimens do occur, the tinder fungus usually produces multiple fruiting bodies on the same tree or log, and adjacent ones sometimes fuse together as they grow. Interestingly enough, if a tree that a tinder fungus is growing on falls down, the fungus will re-orient its direction of growth to account for its changed position, so specimens are sometimes seen with two different patterns of growth in the fruit body, at right angles to each other. This is to ensure that the fertile underside is always aligned with gravity so that the spores will fall into the air currents.
Tinder fungus is a heart rot fungus and a parasite of trees that are already weakened, for example by injury or drought. It is unable to colonise a tree's freshly-wounded sapwood by itself, but will grow in the tree's dead heartwood, or in sapwood that has previously been infected by bacteria or other fungi. As the fungus spreads, the tree eventually dies and the tinder fungus then becomes saprotrophic, helping with the breakdown of the tough cellulose and lignin in the wood. Tinder fungus fruiting bodies only appear once the tree it is growing on has died.
Tinder fungus is hard and woody and can persist for many years, with one fruiting body estimated to have been 22 years old. Although it can often be seen on rotting logs, the fungus itself is rot resistant, because it has the ability to produce compounds with anti-pathogenic characteristics. In practice though, the fungus dies in many cases because the wood it is growing on has reached the stage of advanced decay where there aren't enough nutrients or sufficient fibrous structure to support it any more.
The underside of the tinder fungus consists of a dense concentration of tubes or pores that are cream or pale brown in colour, and about 0.3 mm across. The pores replace the function of gills in most mushrooms, and give rise to the name polypore for the bracket fungi and bolete fungi that possess them. A new layer of tubes or pores is produced annually, and it is from these that the spores are released in May and June each year. The spores are microscopic in size and produced in prodigious quantities - one study recorded 800 million being released in an hour! The spores are distributed by the wind and will begin growing when they land on dead wood, such as the stumps from broken branches or stem scars on a tree.
The woody fungal body (or sporocarp as it is technically known) that grows out of the dead wood is the fruiting body of the species - the main part of the fungus is the network of filaments or hyphae that grow within the tree's wood itself.
Tinder fungus contributes towards the dynamic and changing nature of forests through its role in the mortality of trees. The death of a tree helps to create gaps in the forest, thereby allowing more light-demanding species of tree and shrub to become established. Standing dead trees (also known as snags) such as birch provide nesting sites for various species of birds, and are also an important food source for many species of dead-wood dependent invertebrates.
As a saprotrophic species, the tinder fungus plays an important role in breaking down the cellulose and lignin stored in a tree's wood, making the nutrients it contains available for other species in the forest ecosystem. This recycling also applies to the tinder fungus itself, which is decomposed in part by another fungus (Amblyosporium botrytis). Another nine species of fungi have been recorded growing on tinder fungus, including cobweb mould (Hypomyces rosellus).
A number of beetles are closely associated with tinder fungus, including the black tinder fungus beetle (Bolitophagus reticulatus), whose larvae live inside the fruiting bodies, and the forked fungus beetle (Bolitotherus cornutus), the larvae and adults of which both feed on the fungus - the adults also help to disperse the fungal spores. Two rare Red Data Book-listed beetles (Cis dentatus and Rhopalodontus perforatus) that occur in association with the black tinder fungus beetle have been recorded in Glen Affric. Another species that lives in association with the black tinder fungus beetle is a mite (Boletoglyphus boletophagi). The mite feeds in the tubules or pores of the tinder fungus and its nymphs or larvae are phoretic on the beetle, meaning that they attach themselves to the adult beetle and use it for transport to new host fungi. Another beetle associated with the fungus is Triplax russica , and the adults of this species, which has been recorded on Dundreggan, are often seen sitting on the upper side of the fruiting bodies. One study in Norway identified 35 different species of beetles as living in the sporocarps of the tinder fungus.
The larvae of several moth species overwinter in bracket fungi in Scotland, and at least one of those (Archinemapogon yildizae) utilises tinder fungus for this purpose.
The tinder fungus has also had a long relationship with humans, and both its common and scientific names reflect its usefulness as a good source of tinder for starting fires. The body of the 'Iceman' found preserved in a glacier in the Alps in 1991, and dating back to over 5,000 years ago, was accompanied by a pouch containing flint and a piece of dried tinder fungus, indicating that it played an important role then in people's use of fire.
Tinder fungus is also the source of amadou, a substance utilised by fishermen to extract moisture from the flies they use as bait. The fungus has also long been known to have important healing properties, and in 400 BC Hippocrates referred to it as being used as an anti-inflammatory. Recent studies have found that it has strong anti-viral and anti-bacterial properties, thereby confirming its age-old use.
Alan Watson Featherstone
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