Tremella mesenterica Known as yellow brain, golden jelly fungus, yellow trembler, and witches’ butter.) This specimen was growing in the Forestof Dean.
This species is parasite of wood decay fungi in the genus Peniophora. So whist it is usually observed to be living on dead twigs and branches, it is actually living on a fugus which in turn is living on the dead branches.
It grows in crevices in bark, appearing during rainy weather. Within a few days after rain it dries into a thin film or shriveled mass capable of reviving after subsequent rain. This fungus occurs widely in deciduous woodland and here it was growing on Oak but the small branch on to which it was attached did appear to be alive and healthy…. so that does not exactly fit the classic description.