Witch's Butter Identification Guide

First impressions and the setting

Witch's Butter announces itself by colour. On a grey wet day in a bare winter wood you catch a splash of bright egg-yolk yellow or deep orange on a dead branch, glistening as though someone had squeezed a blob of jelly onto the bark. It is one of the few genuinely conspicuous fungi of the cold months, and its colour carries at ten or twenty paces.

The setting is usually specific: dead but still attached branches of broadleaved trees, particularly on standing dead wood, brash piles and fallen limbs where the bark is still in place. Gorse stems, hazel, beech, oak, birch, ash and willow are all common hosts. It is a fungus of damp weather, and after a dry spell you will find only shrivelled crusts where the jelly was.

Reading the fruit body

There is no cap, no gill, no stem and no pore surface. What you have is an irregular gelatinous mass, and the whole identification rests on its form, colour, texture and behaviour.

The fruit body starts as a small pustule or blob emerging from a bark crack, then expands into a lobed, folded, contorted cushion two to ten centimetres across, occasionally larger where several have coalesced along a split. The folds are broad, rounded and convoluted, and the standard comparison is to a small brain, a pile of soft petals, or a spoonful of dropped jelly. Individual lobes are typically flattened and gyrose, with rounded edges rather than sharp margins.

Attachment is by a narrow point or short line where the mass emerges from the bark, so a fresh fruit body often looks stuck on rather than growing out.

Colour and surface

Colour ranges from pale yellow through bright golden-yellow to deep orange, occasionally with almost apricot tones in the thickest folds. Well-hydrated specimens are translucent, so light passes through the lobes and the fungus glows; the interior can be seen as slightly paler than the surface. Thin exposed edges are often paler, sometimes almost whitish.

Age and sun exposure fade the colour towards dull ochre, buff or pale straw, and very old material can bleach almost white before collapsing.

The surface is smooth, moist and shiny to slightly greasy when hydrated, with no visible ornamentation, no veins and no separate hymenophore - the entire outer surface bears the spore-producing layer. Under a lens it is featureless, and that is itself a character, because the absence of any differentiated fertile surface separates jelly fungi from almost everything else.

Texture and the drying test

This is the test that finishes the identification, and it is easy to run.

Pinch a lobe. Hydrated material is soft, gelatinous, slippery and distinctly elastic - it deforms and springs back, and it can be stretched slightly without tearing. It is not rubbery-firm like some black jelly fungi, nor is it fleshy or brittle.

Now consider what happens in dry weather. The fruit body shrinks dramatically, drawing down into a hard, dark orange to reddish-brown or almost blackish varnished crust that clings to the bark and looks like a scab or a splash of dried paint. Most people never realise this is the same organism. Wet it, or wait for rain, and within a few hours the crust rehydrates and reinflates into the full golden jelly, apparently unharmed. This ability to revive repeatedly through wet and dry cycles is a defining behaviour, and it is why the species can be found in every month of the year.

Cut the fruit body and there is no internal differentiation: it is uniform, translucent and pale yellow throughout, with no colour change on cutting, no latex and no bruising.

Taking and reading a spore print

Jelly fungi print, though it takes patience and fresh, well-hydrated material. Cut off a lobe with a sliver of bark, set it on white paper or a glass slide, cover it with a bowl or box to keep the air saturated, and leave it overnight.

The deposit is white to very pale yellow, thin and easily missed - it often shows better as a faint bloom on dark glass than on paper. Colour alone will not separate it from its close relatives, so the print serves mainly to confirm you are dealing with a basidiomycete jelly rather than a coloured slime mould or an ascomycete crust.

With a microscope, the basidia are the decisive structure: they are longitudinally septate into four cells, the cruciate-septate form that characterises the genus. Spores are broadly ellipsoid to subglobose, smooth and thin-walled.

Substrate, ecology and season

The substrate observation that most people record is simply dead attached broadleaf branches, and that is correct as far as it goes. The more interesting truth is that this fungus is a parasite of other fungi. Its mycelium invades the mycelium of wood-rotting crust fungi, chiefly Peniophora species, that are already colonising the branch. The wood is the arena; the crust fungus is the actual partner.

This has a practical consequence in the field. Look at the bark around and beneath the yellow jelly and you will often find a thin, smooth, pinkish, greyish or lilac-tinted crust spreading over the branch. Finding that crust strongly supports the identification and explains why the jelly appears in the same spots year after year.

Season is effectively year-round, with a strong bias towards autumn, winter and early spring, when humidity is high and the fruit bodies stay hydrated for weeks. Mild wet winter weather produces the best displays. Fruit bodies commonly appear in rows along a bark split, following the crust fungus beneath.

Separating it from the look-alikes

Dacrymyces stillatus is the commonest confusion. It forms much smaller, orange to yellow cushions or discs, usually only a few millimetres across, often in dense scattered troops, and is typically on conifer wood, including worked timber, fence rails and old planks. It lacks the large convoluted brain-like folds, and microscopically its basidia are tuning-fork shaped rather than cross-septate.

Dacrymyces chrysospermus grows on conifer wood, is larger and paler orange, and has a distinct whitish attachment point where it emerges from the wood.

Tremella aurantia is the hardest field call. It is a deeper orange, usually a little firmer, and crucially it parasitises Stereum hirsutum rather than Peniophora, so look on the branch for the hairy, zoned, bracket-forming crust of Stereum rather than a smooth pinkish Peniophora film. Substrate fungus is the practical separator.

Tremella lutescens and pale forms are whitish to very pale yellow and more translucent, with the same folded form.

Naematelia encephala produces pale ochre to pinkish lobes with a firm white core visible when sliced - cut it open and the differentiated centre is decisive.

Exidia species share the gelatinous habit but are black, dark brown or olive-grey, and several have a warted or pimpled surface.

Yellow slime moulds in the plasmodial stage can look similar on wet wood, but they are structureless slime that flows and lacks discrete lobes, and they change form over hours.

Quick field checklist

Bright yellow to orange gelatinous mass, brain-like convoluted folds, translucent and elastic when wet, shrinking to a hard dark crust when dry and reviving when rewetted, on dead attached broadleaf branches, with a thin crust fungus visible on the same bark, and a white to pale yellow spore deposit.