This morning I discover the species as well. It is Armillaria mellea, a Honey fungus. They are parasitic fungi that live on the trees, both dead and living. As fungus itself, it is very interesting. It is one of the largest living fungus on Earth. It's mycelium can cover a space of 10 km2 and be more than thousand years old!
Near the tree trunk.
Older specimens on the tree trunk.
The fungus spreads by means of root-like rhizomorphs, that grow into the wood. That's how it spreads the infection. It spreads about 1 m2 a year, relatively close to the soil surface. So it invades roots and makes a root collar which has happened to my walnut tree. Once the tree is completely girdled it will die. So, I decided to spear my walnut further torment and it goes down this winter. The thing is, the fungus may invade other trees and shrubs and destroy them. It is not dependent of the living host because it grows on the rotten, dead wood too. I am a bit worried - how to kill the mycelium?
Right now it appeared in great number in park and forests. It is really a fantastic sight when almost every stump is covered with their fruit bodies - mushrooms. The mushroom is actually edible though, some would rather avoid it. To some people it may cause digestive problems. I eat it, but cook it first for a few minutes in boiling water (which is to be spilt away, of course).
The fungus comes in several varieties and species as well. Here, there are some photographs I took over the years.