Rhizomorphs of Honey fungus, Armillaria mellea, on a fallen sycamore tree (Acer pseudoplatanus). The picture shows the surface of a trunk that has lain on the ground for several years, and which has lost its bark. The background (pale brown hues) is the trunk of the tree; the black "bootstrap" structures are the fungal rhizomorphs. No bark is visible. A. mellea is 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. It can also live as a saprotroph on decaying or fallen wood