Black Witches' Butter (Exidia glandulosa): Black Witches' Butter. Jean-Baptiste Francois Bulliard, a French naturalist, first recorded this strange fungus in 1789. Named as such for its color and greasy consistency in wet weather, Black Witches' Butter appears on dead hardwood during the autumn and winter seasons. Alternately, in hot and dry weather, these mushrooms appear more greenish-brown and crusty. Also known as Black Jelly Roll, this strange mushroom might have magical powers. Growing singly or in clusters on dead trees — typically oak, hazel, or beech — this bizarre mushroom appears gelatinous in its consistency. It appears to melt in wetter weather and hardens when dry, meaning it is a hardy grower most everywhere on the globe, though particularly in North America and Europe. Also known as Black Jelly Roll or Warty Jelly Fungus for its appearance, another possible origin for its witchier name may be in its supposed power in counteracting witchcraft if thrown into a fire.