Exidia nigricans

What You Should Know

Exidia nigricans 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.

This mushroom forms dark sepia to blackish, rubbery-gelatinous fruit bodies that are button-shaped and around 2 cm (0.79 in) across. The fruitbodies occur in clusters and quickly coalesce to form effused, irregular masses 10 cm (3.9 in) or more across. The upper, spore-bearing surface is shiny and dotted with small pimples or pegs. The individual fruitbodies are each attached to the wood at the base.

Exidia nigricans is a wood-rotting species, typically found on dead attached branches of a wide range of broadleaf trees. It persists for some while on fallen branches and logs. The species typically fruits in autumn and winter. It is widely distributed in the northern hemisphere, including North America and Europe.

Other names: Witches' Butter.

Exidia nigricans Mushroom Identification

1. Fruitbody

   Shiny black when wet, turning olive-brown and shriveling to a warty crust during very dry weather. Individual fruitbodies blend into one another like the folds of a brain; composite 'blobs' are typically 5 to 15 cm across.

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

2. Spores

   Allantoid (sausage-shaped), smooth, 14-19 x 4.5-5.5µm; inamyloid.

3. Spore Print

   White.

4. Odor and Taste

   Not distinctive.

5. Habitat & Ecological Role

   Saprobic, on dead and decaying hardwood - mainly Beech, Ash and Hazel but very occasionally also oaks.

Exidia nigricans Look-Alikes

1. Exidia glandulosa

   Comprises irregular flattish-faceted separate blocks of black jelly-like material.

2. Tremella mesenterica

   Has yellow and has a brain-like structure.

3. Exidia glandulosa

   Top-shaped fruitbodies that rarely if ever coalesce. They are indistinguishable microscopically, but DNA research indicates they are distinct.

4. Tremella foliacea

   Usually a warmer, lighter brown, but can sometimes be dark sepia to black. Its fruitbodies are gelatinous, but usually foliaceous (with flattish lobes or fronds) and never have warts or pegs on the surface. It is common and occurs on both broadleaf trees and conifers.

Exidia nigricans Taxonomy and Etymology

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 Exidiaceae.

The basionym dates from a 1776 publication by British botanist and mycologist William Withering (1741 - 1799). It was the Dutch mycologist Marinus Anton Donk (1908 - 1972) who in 1966 redefined the Exidia genus, clearly separating Exidia plana (now Exidia nigricans) from its lookalike Exidia glandulosa.

British mycologist Peter Roberts suggested that Exidia plana were an invalid name, and that Tremella nigricans With. was the earliest valid name for this species. The official name in the Fungus Records Database for Britain and Ireland now has the preferred name of this species listed as Exidia nigricans.

Synonyms of Exidia nigricans include Exidia plana (Donk) and Tremella plana F.H. Wigg., and Tremella nigricans With.

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.

Sources:

Photo 1 - Author: Michel Langeveld (Creative Commons Attribution-Share Alike 4.0 International)

Photo 2 - Author: E rulez (Creative Commons Attribution-Share Alike 3.0 Unported)

Photo 3 - Author: Garrett Taylor (Creative Commons Attribution 4.0 International)