Exidia glandulosa

Description

Have you ever been walking through a deciduous forest and wondered what those black, tar-like looking structures are that grow on fallen trunks and branches? Well, Exidia glandulosa also known as Black Witches Butter would be a good guess. This fungus is more often recognised during wetter months as it dehydrates during dry weather and shrinks to a dry, shiny and only millimetre thin membrane on the substrate surface. However, the fungus quickly recovers to a soft gelatinous blob in rainy weather.

These jelly fungi are described by Peter Roberts (a professional mycologist formerly working at Kew Gardens) to have 'turbinate fruit bodies (like an old fashioned spinning top)'. They are often higher than wide, can merge with adjacent fruit bodies and become less stable with age, often starting to hang downwards with age. The upper surface ranges in colour from a shiny black to a dull olive brown and is usually smooth with pit-like depressions and glandular warts (see photo), ranging between 10-60 mm in size and occasionally possessing a stalk.

There are several different ideas concerning the derivation of the name Black Witches Butter. One legend from Eastern Europe is linked to the occurrence of the fruit bodies on wooden house entrances, which was thought to indicate that the house was under a witches spell. To counteract this spell, the fungus had to be punctured to allow the ‘evil juices’ inside the fungus to leak out. Other legends record its use against witchcraft when thrown into fires. Despite the name suggesting edibility (albeit somewhat tenuously), Black Witches Butter lacks a distinctive taste and is considered to be inedible.

Occurrence

The fungus can be found throughout the year but is more recognisable during wet weather as they often dry out during summer months.

The similar Exidia nigricans, by Liz Holden