Bulgaria inquinans - Black Bulgar is a very common ascomycete. It is particularly common on Oak, as here, but also other deciduous trees. I usually find it on fallen branches which have obviously been on the ground for some time. The trunk of this tree broke about 5m from the base and these fb's would have been about a further 5m up from the break. This break happened last winter (see Blog 26.4.2016 --- Perriporia fraxinia, on another Oak nearby that fell during same storm) so the trunk has only been on the ground for about 6 months. Has this patch of Bulgaria recently colonised the fallen tree or were they present high up before the tree broke?
This fungus has a host of common names in addition to Black Bulgar ---- eg., Popes Buttons. It seems to have interesting chemical properties. An alcoholic extract has been shown to affect histamine ---- so stops itching in mice (antipruritic and antierythematous effect). The fungus also has the chemicals bulgariclactane -A and -B which kill nematodes. A water soluble polysaccharide has anti-malarial activity in malaria-bearing mice. All usefull stuff!
Although considered a delicacy in parts of China it is best avoided due to reports of unpleasant effects --- poisoning.