Armillaria solidipes Peck, 1900
Common names: Honey mushroom [En], Armillaire d'Ostoya, Armillaire sombre [Fr], Sombere honingzwam [Nl], Dunkler Hallimasch [De]
Tervuren, BRABANT ● Belgium
Taxonomy: The species was formerly known as Armillaria ostoyae Romagn., until a 2008 publication revealed that the species had been described under the name Armillaria solidipes by Charles Horton Peck in 1900, long before Henri Romagnesi had described it in 1970.
Description: The fruiting bodies of Armillaria solidipes (formerly Armillaria ostoyae) are cream to brown-coloured mushrooms with a 5-10 cm wide cap and a distinct ring on the stem).
Biology: The mushrooms are produced from late summer to mid-autumn around the base of infected, living trees, killed trees, and colonized stumps. Fruiting bodies are also commonly growing from dead wood associated with scars on living trees .Armillaria solidipes grows and spreads primarily underground and the bulk of the organism lies in the ground, out of sight. Therefore, the organism is not visible to anyone viewing from the surface. It is only in the autumn when this organism will bloom “honey mushrooms”, visible evidence of the organism lying beneath. Low competition for land and nutrients have allowed this organism to grow so huge and become arguably the largest living organism. A mushroom of this type in the Malheur National Forest in the Strawberry Mountains of eastern Oregon, U.S. was found to be the largest fungal colony in the world, spanning 8.9 square kilometres (2,200 acres) of area. This organism is estimated to be 2,400 years old. While an accurate estimate has not been made, the total mass of the colony may be as much as 605 tons.
The mycelium attacks the sapwood and is able to travel great distances under the bark or between trees in the form of black rhizomorphs ("shoestrings").
This fungus, like most parasitic fungi, reproduces sexually. The fungi begin their life as spores, released into the environment by a mature mushroom. In the specific case of Armillaria solidipes, it has a white spore print in which all the spores are stored until they are released and dispersed. There are two types of mating types for spores (not male and female but similar in effect). The spores can be dispersed by environment factors such as wind or they can be redeposited by an animal. Once the spores are in a resting state, the single spore must come in contact with a spore of an opposite mating type and of the same species. If the single spore isolates are from different species, the colonies will not fuse together and they will remain separate. When two isolates of the same species but different mating types fuse together, they soon form coalesced colonies which become dark brown and flat. With this particular fungus it will produce mycelial cords also known as rhizomorphs. These rhizomorphs allow the fungus to obtain nutrients from long distances away. These are also the main factors to its pathogenicity. As the fruiting body continues to grow and obtaining nutrients, it forms into a mature mushroom. Armillaria solidipes in particular grows a wide and thin sheet-like plates radiating from the stem which is known as its gills. The gills hold the spores of a mature mushroom. This is stained white when seen as a spore print. Once spore formation is complete, this signifies a mature mushroom and now is able to spread its spores to start a new generation.
Habitat: Armillaria solidipes is quite common on both hardwood and conifer wood in forests.
Distribution: Europe, North America.
Caution: This species is considered not edible.
Wikipedia, Armillaria solidipes