Fruiting bodies of honey fungus, Armillaria mellea, on a fallen birch tree. The picture shows a colony of toadstools of A. mellea in October in the UK. The thin parallel woody stems (bottom) are of common ivy, Hedera helix. In this situation A. mellea is behaving as a saprophyte - living on dead wood. But it is also a virulent pathogenic fungus that can infect the roots of a wide range of woody plants as well as some herbaceous plants. It spreads through the soil by means of rhizomorphs, which can extend annually for several metres seeking new hosts. It can present a serious problem in gardens, as treatment is difficult and infection usually fatal to the host. Susceptible hosts in gardens include apples, hawthorn, birch, lilac and privet. Honey fungus is edible, but an acquired taste.