🍄 Introduction

Exidia glandulosa, commonly known as black witch's butter or black brain fungus, is a dark gelatinous basidiomycete forming glossy, blackish-brown, brain-like fruitbodies on dead hardwood branches, particularly oak and ash. A saprotrophic wood decomposer in the order Auriculariales, it is most conspicuous during autumn and winter wet weather when its dark, glistening fruitbodies swell to full size. Though edible and non-toxic, its lack of flavour and unusual rubbery texture limit culinary appeal.

The fruitbody is a gelatinous, irregularly shaped, cushion-like to brain-like mass, 1-5 cm across individually but often coalescing into larger confluent patches up to 20 cm along a branch. The colour is dark olive-brown to jet black, with a glistening, vitreous surface when wet that often bears small, wart-like glandular projections (the glandulosa of the name). The texture is firm-gelatinous, rubbery and elastic when hydrated, becoming hard, shrunken, and almost invisible when dry. The underside is typically paler and smoother where it attaches to the bark substrate.

Quick Facts

🔍 Identification Guide

Search dead hardwood branches, especially oak and ash, during wet weather for dark black-brown gelatinous blobs with a glossy, wet appearance. Use a hand lens to check for the characteristic small wart-like glands on the upper surface, which distinguish E. glandulosa from the smooth E. nigricans. The fruitbody should be firmly gelatinous, springing back when pressed, and dark black-brown throughout without a whitish interior core. Check that the substrate is hardwood, not conifer, to exclude Exidia saccharina.

Morphological Features

Detailed Morphology

The fruitbody surface is covered with minute glandular warts or papillae that appear as small raised bumps under a hand lens, distinguishing this species from the smooth-surfaced Exidia nigricans. The hymenium covers the exposed upper surface including the glandular projections. Basidia are longitudinally to obliquely septate, characteristic of Auriculariales, producing four sterigmata with curved epibasidia. The internal structure is composed of densely interwoven, thin-walled hyphae embedded in a gelatinous matrix. Clamp connections are present.

🧬 Taxonomy & Classification

Exidia glandulosa (Bull.) Fr. was originally described by Bulliard in 1789 and transferred to Exidia by Fries. The species belongs to family Auriculariaceae within order Auriculariales, part of the heterobasidiomycete lineage characterised by septate basidia. The taxonomy of European Exidia has been extensively revised, with E. nigricans (previously E. plana) now recognised as distinct from E. glandulosa based on smooth versus warted surfaces and molecular data. North American collections may include undescribed cryptic species currently filed under the European name.

⚕️ Edibility & Safety

Exidia glandulosa is edible and non-toxic but generally considered not worthwhile due to its bland, essentially flavourless character and unusual rubbery-gelatinous texture. It can be consumed raw or cooked without any safety concerns. In Chinese cuisine, the closely related Auricularia species are highly valued, and Exidia can be used as a substitute when these are unavailable. The fruitbody absorbs flavours from broths and sauces effectively, so it functions best as a textural ingredient in strongly flavoured dishes.

⚠️ Look-Alikes & Confusions

Exidia nigricans (formerly E. plana) is the most commonly confused species, differing in having a smooth surface without glandular warts and typically forming flatter, more effused fruitbodies. Exidia recisa is smaller, more cup-shaped, and lighter brown, typically on willow branches. Auricularia auricula-judae (jelly ear) is reddish-brown, distinctly ear-shaped, and has a velvety outer surface. Bulgaria inquinans (black bulgar) is similar in colour but has a firm, rubbery texture and produces black staining spores.

Known Look-Alikes

🌲 Habitat & Ecology

Exidia glandulosa is a saprotrophic wood decomposer primarily colonising dead branches of Quercus (oak), Fraxinus (ash), and other hardwood species while still attached to the tree or recently fallen. It is among the first fungi to colonise recently dead branches, playing a role in early-stage wood decomposition. The species is widespread across temperate regions of Europe, North America, and Asia, tolerating a broad range of conditions from lowland to montane forests. It is particularly abundant in humid Atlantic and oceanic climates with mild winters.

Ecological Role

Exidia glandulosa is an important early coloniser of dead hardwood branches, initiating the decomposition process that will eventually break down the wood through successive fungal communities. Its enzymatic activity softens bark and sapwood, facilitating colonisation by subsequent decomposer fungi, insects, and other organisms. The gelatinous fruitbodies retain moisture on branch surfaces, creating humid microhabitats for invertebrates, bryophytes, and other organisms. The species contributes to nutrient cycling by slowly releasing minerals locked in dead wood back into the forest ecosystem.

🗺 Distribution Map

Known distribution of Witches' Butter: Europe, North America, parts of Asia. This species is saprotrophic (Saprotrophic).

🧺 Foraging Guide

Exidia glandulosa is extremely common and easy to collect in any deciduous woodland during wet weather from October through March. Look on dead branches at eye level and above, where the dark gelatinous blobs are conspicuous against pale bark when wet. Collect by peeling fruitbodies from branches or cutting small branch sections. Gather generous quantities since the fruitbodies shrink considerably during cooking. The species is superabundant in most woodland and there are no conservation concerns about harvesting.

🌱 Cultivation

Exidia glandulosa has not been commercially cultivated, though its saprotrophic ecology makes it theoretically amenable to cultivation on sterilised hardwood substrate. The closely related Auricularia species are successfully cultivated on sawdust blocks worldwide, suggesting similar techniques could work for Exidia. Experimental cultivation on oak sawdust supplemented with wheat bran has produced mycelial growth but fruiting has been inconsistent. Given the species' abundance in the wild, there is little economic incentive to develop cultivation methods.

🍳 Culinary Uses

Exidia glandulosa is best used as a textural addition to Asian-style soups, hot pots, and stir-fries where it absorbs surrounding flavours while contributing a unique bouncy, slightly crunchy mouthfeel. Rinse collected fruitbodies thoroughly, slice into strips, and add to dishes in the final few minutes of cooking. It can substitute for wood ear mushroom (Auricularia) in recipes at roughly double the volume since Exidia has a softer texture. The dark colour adds visual drama to clear broths and noodle dishes.

📦 Preservation & Storage

Fresh fruitbodies keep for about a week in the refrigerator in a sealed container, slowly losing moisture but remaining usable. Drying is the optimal preservation method: spread fruitbodies on a rack at room temperature or use a dehydrator at 40 degrees Celsius until they shrink to hard, dark chips. Dried Exidia glandulosa reconstitutes remarkably well when soaked in warm water for 20-30 minutes, regaining its gelatinous texture and dark glossy appearance almost completely. This exceptional rehydration property makes it ideal for long-term pantry storage, lasting over a year when kept dry.

🩹 Medicinal Properties

Exidia glandulosa has received limited pharmacological study compared to its commercially important relative Auricularia auricula-judae. Preliminary research has identified polysaccharides with potential antioxidant and immunostimulatory activity in crude extracts. The gelatinous matrix contains glucomannans similar to those in Tremella species, which may have prebiotic and skin-health properties. Traditional European herbalism did not apparently utilise this species, and no established medicinal applications exist.

🍂 Seasonal Fruiting

Exidia glandulosa fruits primarily from October through April in temperate regions, with peak abundance during the wettest months of November through February. It is one of the most reliable winter-fruiting fungi, appearing even during cold snaps when temperatures hover just above freezing. In mild oceanic climates, fruiting can occur year-round during prolonged wet periods. The fruitbodies respond rapidly to moisture, desiccating to inconspicuous crusts during dry spells and rehydrating within hours of rainfall.

🔬 Spore Print & Microscopy

Spores are allantoid (sausage-shaped), 10-16 x 4-5 micrometres, smooth, hyaline, thin-walled, and often containing oil droplets visible under high magnification. The spore print is white. Basidia are subglobose to pyriform, longitudinally to obliquely septate into four cells, each producing a curved epibasidium bearing a single basidiospore. The glandular warts on the fruitbody surface contain clusters of hyphae with refractive contents visible in section under the microscope. Internal hyphae are thin-walled and gelatinised, with clamp connections.

🌀 Varieties & Forms

Fruitbody morphology varies considerably depending on moisture conditions, substrate orientation, and branch diameter. On horizontal branches, fruitbodies tend to be more cushion-like and symmetrical, while on vertical surfaces they may be more effused and irregular. Extremely wet conditions produce larger, more translucent fruitbodies, while marginal moisture results in smaller, more opaque forms. Some collections on ash develop a distinctly more olive-toned coloration compared to the jet-black typical of oak-growing specimens.

📜 History & Ethnomycology

The name witch's butter for dark gelatinous fungi has deep roots in northern European folklore, where mysterious jelly-like substances appearing on wood were attributed to witchcraft or evil spirits. In Swedish folk tradition, dark Exidia on door frames was called trollsmor (troll's butter) and was considered an ill omen. Bulliard's 1789 description made it one of the earlier formally named jelly fungi. In eastern European folk medicine, dark jelly fungi were occasionally applied as poultices to swollen joints, though no efficacy has been demonstrated.

🎓 Beginner's Guide

Exidia glandulosa is an excellent winter identification target because it is extremely common, present when few other fungi are fruiting, and its dark gelatinous form on dead branches is highly distinctive. Visit any deciduous woodland after rain between November and March and scan dead branches for shiny black jelly blobs. Use a hand lens to check for the tiny wart-like bumps on the surface. Practice distinguishing it from the smooth-surfaced Exidia nigricans, as learning to tell these two apart is good training in careful observation.

Photography Tips

The glossy black surface of Exidia glandulosa is challenging to photograph due to high contrast and specular reflections. Use diffused lighting or overcast conditions to reduce harsh glare on the wet surface. Side lighting at a low angle reveals the glandular wart texture that is diagnostic for the species. Include the bark substrate and several fruitbodies to show the coalescent growth pattern. A macro shot of the glandular surface with a droplet of water catching the light creates a compelling detail image. Shoot after rain for maximum photogenic impact.

Common Mistakes

Troubleshooting

If your Exidia collections lack visible glandular warts, ensure you are examining fresh, hydrated material under a hand lens, as the warts can be subtle on young fruitbodies. Completely smooth-surfaced dark jelly on hardwood is likely Exidia nigricans rather than E. glandulosa. If fruitbodies seem to vanish from known locations during dry weather, look carefully for hard, shrunken dark crusts on the same branches, which will rehydrate with the next rain. Amber-coloured rather than black jelly on conifer wood indicates Exidia saccharina, not E. glandulosa.

❓ Frequently Asked Questions