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Winter 2013

Urban Jungle

The changing natural world at our doorsteps | Illustration and text by Patterson Clark      

January 8, 2013

Horse hoof fungus: A shelf fungus that can blossom into flame


In even the harshest winter, the common horse hoof fungus persists in the landscape, its fruit jutting from the trunks of hardwood trees. Inside the tree, a vast fungal infection consumes the heartwood. Fine threads of the "white rot" will continue to feed on the tree even after it falls.

After the tree hits the ground, the woody, spore-bearing fruit — resembling a horse's hoof — responds to its altered orientation to gravity by sending a new fruit out of the old one, adjusting its position so that the spore surface faces down:

Horse Hoof Fungus, Fomes fomentarius

In the winter the hoof doesn't grow, but come spring it will resume expansion of its spore-producing surface at the margins. A hoof can grow for many years before tunneling beetles finally consume it.

The hoof attracts numerous mites and insects, which become dusted with fungal spores. The arthropods

can then transfer the infection to another tree by crawling over exposed wood, such as that from a broken branch.

Though the fungus is inedible for humans, people sometimes harvest the fibrous layer between the hoof's woody crust and its spore tubes. Hammered flat, this amadou can be formed into cloth or used as a highly flammable tinder for starting fires, a technique that has been practiced for millennia.

Amadou was found in the possession of the Tyrolean Iceman, whose 5,000-year-old remains were discovered in 1991, frozen in a retreating alpine glacier on the border between Italy and Austria. His amadou held traces of iron pyrite, which can be used with flint to produce sparks.

Sources: "Fungus-Insect Relationships: Perspectives in Ecology and Evolution," South Tyrol Museum of Archaeology, The Canadian Entomologist, Biodegradation, Entomologica Fennica, Journal of Chemical Ecology

Horse Hoof Fungus, Fomes fomentarius

Underside of old fruit

Fallen tree

New fruit

Crust

Amadou

Spore tubes

Beetle gallery