In a 150-year old treatise on English botany, (Sowerby et al., 1846, p. 225) it is mentioned that according to Dillenius, this species earned its common name "witches' butter" because it was believed to be useful against witchcraft when thrown into a fire.
(Healing-mushrooms.net)
Exidia nigricans (common name Witches' butter) is a jelly fungus in the family Auriculariaceae. It is a common, wood-rotting species throughout the northern hemisphere, typically growing on dead attached branches of broadleaf trees. It has been much confused with Exidia glandulosa.
