Warlock's Butter

Description

Warlock's butter is a gelatinous fungus with black, glossy, folded fruiting bodies, usually a few centimetres across. Young fruiting bodies are greyish and round or cup-shaped; with age they become wrinkled like a brain. Neighbouring fruiting bodies merge into irregular black clusters that look like a spilled mass. When dry they harden and shrink, and after rain they swell up again.

It grows all year round and is most visible in wet weather. It occurs on dead branches of broadleaved trees, often still attached, in various types of forest. In Poland it is common.

It is told apart from similar jelly fungi by the fruiting bodies merging into larger clusters and by the finely warty surface. Exidia pithya grows on conifers, and Exidia glandulosa forms separate, spiny fruiting bodies. These species are very similar to one another and telling them apart can be difficult.

Identification features

Cap

No typical cap; the fruiting body is gelatinous, at first grey, spherical or cup-shaped, up to about 5 cm across, later folded like a brain. The upper surface is finely dotted or warty, glossy and dark: grey-brown, sepia to black. Neighbouring fruiting bodies merge to form effused, irregular clusters up to about 30 cm. Each fruiting body is attached to the substrate at its base. When wet it is soft and translucent-gelatinous; when dried it becomes hard and crust-like, and swells up again when moistened.

Hymenophore (underside of the cap)

No gills, tubes or spines; the spore-bearing layer (hymenium) covers the upper, folded surface of the fruiting body.

Stem

No stem; the fruiting body is sessile, attached by its base to the wood.

Flesh

Blackish to brownish, translucent, gelatinous, odourless. Do not taste it.

Spore print and spores

Spore print colour: no data. Spores cylindrical, curved (sausage-shaped), smooth, about 8–23 × 3–7 µm (descriptions give different ranges).

Habitat and distribution

Ecology. A saprotroph decomposing dead wood; usually on dead branches of broadleaved trees that are still attached, less often of conifers. It also persists for some time on fallen branches and logs.

Distribution. Europe (in the north up to about 55.7° latitude) and New Zealand; its presence in North America is uncertain. Common in Central Europe and in Poland. It occurs in various types of forest, more often in lowlands; in the Polish mountains it reaches about 1000 m a.s.l. It is not legally protected in Poland.

Fruiting. Fruiting bodies appear all year round, especially during wet weather.

What can it be confused with?

• Exidia pithya (Polish: kisielnica smołowata) — Fruiting bodies are also black and gelatinous, but smaller and flat; it grows almost exclusively on conifers.
• Exidia glandulosa (Polish: kisielnica trzoneczkowa) — Fruiting bodies are solitary, barrel-shaped or saucer-shaped, rarely merging; the outer side is covered with spines.
• Exidia friesiana — Surface smooth, without warts; grows only on conifers.
• Exidia truncata — Forms separate, cone-shaped fruiting bodies that rarely merge.

Never rely on a single feature. If you are not sure — do not pick it; show the mushroom to a qualified mushroom expert.

Interesting facts

• In England the species was called witches' butter: it was believed to be butter scattered at night by witches who steal milk from cows. In Sweden it was known as troll's butter.
• A dried fruiting body hardens and becomes crust-like, but swells up again when moistened and regains its gelatinous consistency.
• The first description of the species, as Tremella nigricans, comes from William Withering in 1776.
• The current genus name Exidia together with the epithet nigricans was established by P. Roberts in 2009.