Porcelain Fungus Identification Guide

First Impression and Setting

This is an autumn beech species and you usually see it before you can reach it. Standing in mature beech woodland after rain, you notice pale, glistening discs on a dead standing trunk or on a large limb that is still attached ten metres above you, catching the light like wet glass. Fallen branches bring the same fungus down to eye level, and that is where identification actually gets done. In hand, the first impression is of extreme sliminess: the cap is coated in a thick, colourless, transparent gel that strings between your fingers and makes the mushroom almost impossible to hold. The second impression is translucency, since the flesh is so thin that you can often see the shadow of the gills through the top of the cap.

Reading the Cap

The cap is 2 to 8 cm across, occasionally larger, hemispherical at first and expanding to convex or nearly flat, often with a shallow central depression or a low umbo. Colour is ivory to pure white, commonly with a grey, olive or pale brownish wash over the centre, and the whole thing looks waxy-translucent when soaked. The margin is thin, often wavy or lobed and finely grooved or striate, and it can split in old specimens. The defining surface feature is the gluten: a separable layer of clear slime that can be peeled off as a skin from a fresh cap, thick enough to leave the fungus dripping. Rain intensifies it; a long dry spell can reduce it to a tacky film, which is the main reason this species is occasionally misjudged.

The Gills

Turn the cap over. The gills are white and stay white, broad, thick-edged, and conspicuously distant, with a comparatively small number of full-length gills and short intermediates between them. They are adnate, often with a short decurrent tooth running onto the stipe apex, and their faces are frequently interveined at the base. Their texture reads as slightly waxy and soft rather than papery. The combination of pure white, widely spaced, rather thick gills on a slimy white cap is unusual enough to be halfway to a diagnosis.

The Stipe, Ring and Base

The stipe is 3 to 8 cm long and 3 to 8 mm thick, white, and usually curved or elbowed because the mushroom is correcting its orientation on a vertical trunk so that the cap hangs level. Above the ring it is smooth, dry and often faintly striate. Below the ring it becomes progressively covered with small greyish to pale brown fibrillose scales, and the base is often slightly swollen and attached firmly to the wood.

The ring is a key character and it is easy to miss beneath the slime. It sits high on the stipe, is white and membranous, flares outwards, and is usually persistent, with a grooved or striate upper surface. Wipe the gel away with a leaf before deciding it is absent. There is no volva.

Flesh and Colour Change

Slice a fruit body top to bottom. The cap flesh is white, thin, soft and watery, sometimes barely two millimetres thick, while the stipe flesh is white and more fibrous. Neither changes colour on cutting or bruising: no reddening, no blueing, no blackening. There is no latex.

Taking a Spore Print

Blot the cap gently to remove surface slime, then set it gills-down on dark paper under a cover for four to eight hours. The deposit is white and can be surprisingly heavy, since this species is a prolific sporer; on a good night you will find a white bloom on leaves and branches lying underneath a fruiting trunk in the wood itself. Under the microscope the spores are exceptional: very large, broadly ellipsoid to almost spherical, commonly 13 to 18 micrometres, smooth and thin-walled. Even a modest lens setup shows they are far bigger than the spores of most white-spored gilled fungi, which is a satisfying confirmation.

Substrate and Season

The fungus is a decomposer and weak parasite of beech, appearing on dead standing trunks, attached dead limbs high in the canopy, and fallen branches; other broadleaves are used far less often. It fruits from late summer into late autumn, sometimes lingering after the first frosts, and it is a wet-weather species that shrivels quickly in dry spells. Fruit bodies grow singly, in small groups and in overlapping tiers along a branch, and a single fallen limb can carry dozens. Mature beech woodland with plenty of standing deadwood is the habitat to search.

Separating It From Look-alikes on Morphology

• Oyster mushrooms (Pleurotus) grow in tiers on broadleaf trunks but have dry, non-glutinous caps, crowded decurrent gills, no ring, and a stipe that is lateral, very short or absent altogether.
• Hygrophorus eburneus is white, slimy and waxy-gilled, but it fruits on the ground in mycorrhizal association with beech, its gills are clearly decurrent, its stipe is slimy along its whole length, and it has no ring.
• Hymenopellis (Xerula) radicata is a close relative but has a dry to slightly tacky brown, radially wrinkled cap, no ring, and a long tapering root that runs down into the soil from buried wood.
• Armillaria species have honey to tan caps with dark erect scales, a ring, cream spores, and grow in dense clusters at the base of trunks and over roots rather than as glassy solitary caps on branches.
• Volvariella species on wood have free gills, a pink spore print and a sac-like volva.
• Very young buttons can look like blobs of clear jelly and be mistaken for a jelly fungus; splitting one open reveals a fully formed miniature cap, gills and stipe, which no jelly fungus has.

Field Checklist

On beech wood, often high up or on fallen limbs; cap white to ivory, translucent, coated in thick clear slime; gills white, broad, distant, adnate with a tooth; stipe white and curved, scaly below a persistent membranous ring; flesh thin, white, unchanging; spore print white with unusually large spores; late summer to late autumn.