Exidia glandulosa (Bull.) Fr. - Witches' Butter

Distribution - Taxonomic History - Etymology - Identification - Culinary Notes - Reference Sources

Exidia glandulosa - Witches' Butter

Taxonomy

Phylum: Basidiomycota

Class: Tremellomycetes

Order: Auriculariales

Family: Auriculariaceae

Exidia glandulosa - often referred to as Black Witch's (or Witches') Butter, perhaps because of its butter-like consistency and greasy surface when wet as well as its sombre colour, occurs throughout the year on dead hardwood.

An alternative theory for the origin of the common name of this fairly common jelly fungus is that this species was thought to have the power to counteract witchcraft if the fruitbodies were thrown on to a blazing fire.

Tremella mesenterica - Yellow Brain

In wet weather Exidia glandulosa turns black and jelly like; however, during prolongued dry spells it shrinks to a series of cone-shaped olive-brown crusts. The individual fruitbodies sometimes coalesce to form larger blobs.

Tremella mesenterica (left), generally known as the Yellow Brain Fungus, is also (confusingly) referred to by some authors as Witches' Butter - further justification for using (or at least always including) the scientific name when making a reference to a particular fungus species.

Autumn and winter are the best times to look for both of these jelly fungi (and indeed most other jelly fungi), even though they can fruit at any time of the year.

Distribution

Exidia glandulosa occurs throughout Britain and Ireland, where it is no more than a fairly common find. This fungus can be seen also in many countries on mainland Europe. On a worldwide scale the distribution of Exidia glandulosa is unclear and probably inaccurately recorded, partly because this species was not clearly separated taxonomically from the macroscopically similar Exidia plana until the late 1960s, and even nowadays misidentification is not uncommon. It is quite likely that this jelly fungus is widely distributed throughout the northern hemisphere; it is certainly reported to be widely distributed in North America.

Taxonomic history

The taxonomy of this jelly fungus is unclear, and some authorities still place it in the order Tremellales. In the USA the genus Exidia is placed under the family Auriculariaceae rather than, as in Britain, Exidiaceae.

The fungus that we know as Witches' Butter was originally described in 1789 by the French naturalist Jean Baptiste Francois (Pierre) Bulliard, who gave it the scientific name Tremella glandulosa. Then in 1822 the great Swedish mycologist Elias Magnus Fries transferred this species to the genus Exidia, but unfortunately Fries used the name Exidia glandulosa to cover not only Witch's Butter but also the jelly fungus that we know today as Exidia plana. The separation of these two species was finally clarified by Dutch mycologist Marinus Anton Donk (1908 - 1972) who in 1966 redefined the Exidia genus, clearly differentiating between Exidia plana and Exidia glandulosa.

Synonyms of Exidia glandulosa include Tremella glandulosa Bull., Tremella spiculosa Pers., Gyraria spiculosa (Pers.) Gray, Exidia truncata Fr., and Exidia spiculosa (Pers.) Sommerf.

Exidia glandulosa is the type species of the genus Exidia.

Etymology

Exidia, the generic name, means exuding or staining, and both seem appropriate because these jelly fungi do look like exudations when moist and like dark stains on wood when they dry out. The specific epithet glandulosa comes from Glandul- meaning gland, and the suffix -osa meaning abundant - a reference to the abundance of glands on the surface of the fruitbodies of this jelly fungus.

Identification guide

Closeup of Exidia glandulosa

Fruitbody

Shiny black and gelatinous (but noticeably firmer than Tremella mesenterica, the Yellow Brain, and most other jelly fungi) when wet, turning olive brown and shrivelling to a warty crust during very dry weather. Individual fruit bodies grow to between 1 and 2cm across, sometimes coalescing to create larger masses typically 3 to 10cm across.

Dried and shrivelled fruitbodies are revived in wet weather and regain their expanded shape and gelatinous texture.

Spores of <em>Exidia glandulosa</em>

Spores

Allantoid (sausage-shaped), smooth, 12-14 x 4.5-5µm; inamyloid.

Spore print

White.

Odour/taste

Not distinctive.

Habitat

Saprobic, mainly on dead and decaying hardwood - notable hazel, beech and oak - but very occasionally also on pine.

Season

Throughout the year in Britain and Ireland but most prevalent in late autumn, winter and early spring.

Similar species

Exidia plana has a brain-like structure without well-defined facets; its spores are more elongated than those of Exidia glandulosa, and it occurs more often on Beech, Ash and Hazel wood than on oak.

Tremella mesenterica is yellow and has a brain-like structure.

Culinary Notes

This jelly fungus is of dubious edibility, and in any case it is too insubstantial to be worth collecting for food. We therefore class it as being of no culinary value.

Reference Sources

Pat O'Reilly (2011) Fascinated by Fungi; First Nature

British Mycological Society (2010). English Names for Fungi

Dictionary of the Fungi; Paul M. Kirk, Paul F. Cannon, David W. Minter and J. A. Stalpers; CABI, 2008

Taxonomic history and synonym information on these pages is drawn from many sources but in particular from the British Mycological Society's GB Checklist of Fungi and (for basidiomycetes) on Kew's Checklist of the British & Irish Basidiomycota.