Exidia nigricans

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***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*.

## Taxonomy

The species was originally described from England as *Tremella nigricans* by Withering in 1776, based on a phrase name published by Dillenius in 1741. It was subsequently considered a synonym of *Exidia glandulosa*, until Donk revised species concepts in 1966 and placed it in synonymy with *Exidia plana*. Changes in the starting point for fungal nomenclature has made *Exidia plana* illegitimate, however, leaving *Exidia nigricans* as the earliest name for the species.

Molecular research has shown that *Exidia glandulosa* and *E. nigricans*, though similar, are distinct.

## Witches' butter

Both Dillenius (1741) and Withering (1776) gave the English name for this species as "Witches' butter", though this name has subsequently also been applied to other gelatinous fungi, including *Exidia glandulosa* and the yellow *Tremella mesenterica*. It is said to be based on a folk belief that witches milk cows at night and scatter the butter around. Clearly the butter they produce does not look appetizing. In Sweden, it is apparently known as "Troll smör" ("Troll's butter") for the same reason.

## Description

*Exidia nigricans* forms dark sepia to blackish, rubbery-gelatinous fruit bodies that are button-shaped and around Template:Convert across. The fruitbodies occur in clusters and quickly coalesce to form effused, irregular masses Template:Convert 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. The spore print is white.

### Microscopic characters

The microscopic characters are typical of the genus *Exidia*. The basidia are ellipsoid, septate, 15-25 × 8-13 µm. The spores are allantoid (sausage-shaped), 14-19 × 4.5-5.5 µm.

### Similar species

 File:Exidia glandulosa.jpg
*Exidia nigricans* and *E. glandulosa* are frequently confused. The two are similar, but *E. glandulosa* produces discrete, top-shaped fruitbodies that rarely if ever coalesce. They are indistinguishable microscopically, but DNA research indicates they are distinct.

*Tremella foliacea* is 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.

## Habitat and distribution

*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.

## References

1. ↑ Donk, M.A. (1966). Check list of European hymenomycetous heterobasidiae. *Persoonia* 4: 145–335.
2. ↑ International code for botanical nomenclature http://ibot.sav.sk/icbn/main.htm
3. ↑ 3.0 3.1 Roberts, P. (2009). *Exidia nigricans*: a new and legitimate name for *Exidia plana*. *Mycotaxon* 109: 219–220.
4. ↑ 4.0 4.1 Weiss, M & Oberwinkler, F. (2001). Phylogenetic relationships in *Auriculariales* and related groups – hypotheses derived from nuclear ribosomal DNA sequences. *Mycological Research* 105: 403–415.
5. ↑ Rolfe, R.T. & Rolfe, F.W. (1925). *The romance of the fungus world*. p. 13
6. ↑ 6.0 6.1 Breitenbach, J. & Kranzlin, F. (1986). *Fungi of Switzerland* Vol. 2: 65 (as *E. glandulosa*)
7. ↑ Breitenbach, J. & Kranzlin, F. (1986). *Fungi of Switzerland* Vol. 2: 66

## External links

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