Witches' Butter

Description

Witches' Butter forms gelatinous, brain-like folded fruiting bodies 1–5 cm across, golden yellow or orange, glossy and slimy when wet. It pushes through cracks in the bark of dead branches, usually of deciduous trees such as beech, oak, ash or hazel. In dry weather it shrinks to a thin, dark film, and after rain it swells again.

It is common in Poland. Fruiting bodies appear on damp days throughout the year, most often in late autumn, winter and spring. It grows as a parasite on the mycelium of other fungi of the genus Peniophora, so in effect it is a 'fungus on a fungus'.

It can be confused with Tremella aurantia, which grows only near the hairy curtain crust (Stereum hirsutum), is matt and has thicker lobes, and with Dacrymyces chrysospermus, which grows on conifer wood. The species is not poisonous, but the catalogue regards it as inedible.

Identification features

Cap

No cap in the strict sense: the fruiting body is gelatinous, irregular, rounded, lobed or folded like a brain, 1–5 cm (up to 7.5 cm) across and 2.5–5 cm high. The surface is usually smooth and glossy, slimy and greasy when wet; the lobes are translucent, deep yellow or yellow-orange, golden or cream-lemon, fading with age and partly dissolving, rarely lacking pigment (white). Young fruiting bodies are covered with slime from asexual conidia, which is golden yellow in mass. A wet fruiting body is gelatinous but sinewy; when dry it becomes hard and shrinks to a thin, dark reddish or orange film that revives after rain.

Hymenophore (underside of the cap)

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

Stem

No stem; the fruiting body pushes through cracks in the bark of the substrate, growing from a primordium under the bark.

Flesh

Gelatinous, sinewy when wet, hard when dry. No distinct taste or smell. Do not taste the flesh in order to identify the fungus.

Spore print and spores

Spore print white or pale yellow, non-amyloid. Spores roundish-ellipsoid to oblong, smooth, without a germ pore, about 10–16 × 6–12 µm (descriptions give different ranges). They germinate by a tube or by budding into yeast-like conidia.

Habitat and distribution

Ecology. A parasitic fungus on the mycelium of wood-inhabiting fungi of the genus Peniophora; sometimes fruiting bodies of the host and the parasite grow together. It occurs on dead but still attached or freshly fallen branches of trees, mainly deciduous (beech, oak, ash, hazel; in Canada most often on red alder), less often coniferous. It emerges from cracks in the bark during rainy weather; it prefers habitats from damp to wet.

Distribution. Cosmopolitan: Europe, Asia, Africa, North, Central and South America, Australia; absent from Antarctica. Widespread in the temperate and tropical zones, in deciduous and mixed forests. Common in Poland. Not legally protected in Poland.

Fruiting. Fruiting bodies appear during spells of wet weather throughout the year, most often in late autumn, winter and spring.

What can it be confused with?

• Tremella aurantia (= Naematelia aurantia) — Grows only near the hairy curtain crust (Stereum hirsutum), on which it is parasitic; the surface is usually matt, not greasy, and the lobes are thicker. When dry it keeps its shape instead of shrinking to a film. It has smaller basidia and spores (about 8.5–10 × 7–8.5 µm) and no vesicles; it is less often translucent.
• Dacrymyces chrysospermus — Grows on conifer wood, is smaller and has a pale point of attachment to the substrate. Under the microscope it has forked (Y-shaped), 2-spored basidia rather than basidia divided by longitudinal septa.
• Tremella brasiliensis and Tremella mesenterella — Similar species from the Neotropics and Japan (the former) and from North America (the latter); they have no practical importance in Poland.

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

• The English name 'witches' butter' derives from Swedish and Scandinavian folklore about witches; the name is also used for Exidia glandulosa and for the slime mould Fuligo septica.
• It is the type species of the genus Tremella, described in 1769 by Anders Jahan Retzius.
• When dry it shrinks to a thin film or a shriveled mass, which revives after the next rain.
• It is a parasite of other fungi (Peniophora), not of wood; its life cycle includes a yeast-like phase.