Black Witch's Butter Identification Guide

The Setting

You usually meet this species in poor weather, which is exactly when it looks its best. A wet autumn or winter walk through oak woodland, a dead branch still hanging in the crown or recently fallen across the path, and along its upper side a row of glistening black blobs that look like spilled tar or a smear of very dark jam. Wet, they are plump and shining; dry, they are almost invisible, reduced to a thin black skin welded to the bark. Timing your visit to a damp spell is not optional with jelly fungi, it is the identification method.

Growth Habit Along the Branch

Start by stepping back and reading the colony rather than a single blob. Black Witch's Butter typically begins as separate top-shaped or cushion-shaped bodies, each perhaps 1-3 cm across, dotted along a branch. As they enlarge they run together into an irregular ridged, brain-like mass that can occupy 10-20 cm of the branch, still showing the outlines of the individual cushions within it. Each body narrows to a small attachment point where it meets the bark, so a young specimen can be lifted with a fingernail and comes away leaving a neat little scar.

The Surface Under a Lens

This is where the species earns its scientific name. Bring a hand lens to the upper, exposed surface of a fresh fruit body and you should see it scattered with tiny dark pimples or wart-like papillae, standing slightly proud of the glossy jelly. They give the surface a granular, pin-cushioned look at 10x that is quite different from the plain glassy sheet you get on some relatives. The overall colour ranges from dark olive-black through blackish-brown to pure black, sometimes with a slight translucency at the margin where light passes through the jelly.

Texture and Sectioning

Pinch it. The consistency should be firmly gelatinous and elastic, like stiff jelly or soft rubber, springing back when released rather than crushing to mush. Slice a piece with a knife: the interior is homogeneously gelatinous and translucent black-brown throughout, without a distinct rind, layered flesh or contrasting core. There is no milk, no latex and no colour change on cutting. If your specimen has a leathery or rubbery-but-not-gelatinous feel and a clearly differentiated outer skin, you are probably not in Exidia at all.

The Dry State and the Revival Trick

In dry weather the fruit bodies shrink dramatically, losing most of their volume and drying to a thin, brittle, blackish crust or film that hugs the bark. Many people walk past this stage entirely. If you find a suspicious black varnish on dead oak, wet it thoroughly and come back in a few hours, or take a piece home and soak it in a saucer of water: it will swell back into recognisable jelly. This ability to rehydrate repeatedly through a winter, releasing spores each time conditions turn wet, is what allows a single colony to persist for months.

Spore-Bearing Surface, Print and Microscopy

There are no gills, pores or teeth. The fertile layer coats the whole exposed outer surface of the jelly, which is why the pimples matter: in many descriptions those papillae are treated as sterile projections punctuating a fertile skin. To get a print, lay a fresh, fully hydrated fruit body on dark glass or black card, cover it to keep the humidity up, and leave it overnight in a cool place. The deposit is white and can be surprisingly heavy from a well-soaked specimen. Under the microscope the spores are long, narrow and distinctly curved, the sausage or allantoid shape typical of the group, and the basidia are divided lengthwise into four cells, the classic tremelloid arrangement that confirms this is a jelly fungus rather than a black cup fungus.

Host, Substrate and Season

Look on dead broadleaved wood, overwhelmingly oak, with beech, hazel and other hardwoods as occasional alternatives. Attached dead branches still in the canopy and freshly fallen limbs are far more productive than long-rotten logs on the ground, so scan the standing deadwood in a wood rather than the leaf litter. The main season is autumn through to early spring, with hard flushes after prolonged rain, and it is one of the few conspicuous fungi you can reliably find in midwinter. Fruiting is often gregarious, so once you find one branch, check every dead limb on the same tree.

Separating the Look-Alikes on Structure Alone

Exidia nigricans (often listed as E. plana) is the main confusion and grows in the same places. It tends to form broad, flattened, spreading crusts that fuse early into large convoluted sheets on the branch, rather than discrete cushions with narrow attachments, and its surface is comparatively smooth, without the well-developed pimples. If your specimen is a wide black brain-like sheet with a broad attachment, lean towards E. nigricans; if it is a row of separate warty cushions each pinched at the base, lean towards E. glandulosa.

Exidia recisa shares the gelatinous texture and top-shaped growth but is amber, tawny or reddish-brown and translucent, not black, and favours willow.

Exidia thuretiana is whitish to translucent grey and forms lobed cushions on beech.

Bulgaria inquinans is the classic non-jelly impostor on fallen oak. It forms discrete top-shaped or button-like bodies with a shiny black upper disc, but the outer surface is dull brown and roughly felty or scurfy, and the texture is firmly rubbery rather than wobbling and gelatinous. It also drops a dark brown to black spore deposit, the opposite of the white print of Exidia.

Tremella foliacea is leafy and brown, with frilly upright lobes rather than pimpled cushions, while Auricularia auricula-judae is tan to date-brown, ear-shaped, and veined on its inner face.

Field Checklist

Wet weather; dead attached hardwood, usually oak; discrete black cushions each narrowed at the base and merging into a ridged mass; visible pimples at 10x; firm elastic jelly throughout; white spore print. That sequence gets you there without ever needing a microscope, though the curved spores and four-celled basidia are a satisfying confirmation.