(Those tiny little mushrooms always give me the willies. I just HAVE to take a photo even though I know I will have big troubles determinating them. Today at least I have to offer a guess.
It is probably Omphalina ericetorum - Gefalteter Nabling; if so it is believed - see Rogers Mushrooms - that this one is the reproductive stage of a half-lichen called Botrydina vulgaris: a lichen where only a loose connection between fungi-part and algae-part of the lichen exists, therefore half-lichen, and where the fungi-part allegedly would produce this mushroom occasionally. I do not know if this is true; I'll have to look into the matter closely, especially search for Botrydina vulgaris.)
