Ceramic Parchment Identification Guide

The First Impression

Ceramic Parchment is a fungus you find by looking at wood rather than at the ground. The classic encounter is on a long-dead oak: a fallen trunk that lost its bark years ago, a weathered stump sawn flat, the exposed heartwood of a split limb, sometimes an old oak gatepost or rail. The wood is grey, hard, sun-dried and often ringing-solid when you knock it. Across that surface runs a pale crust that, from a metre away, reads as a patch of dried whitewash or a smear of pale mortar. Step closer and the illusion collapses into something much more distinctive: the crust is divided into hundreds of small flat tiles separated by dark cracks, exactly like crazed glaze on old ceramic or a dried mud pan seen from the air.

That mosaic is the whole identification. Almost nothing else on wood breaks itself into such regular little plates. Once your eye has learned the pattern you will pick it up at walking pace on any woodland ride where big oak is left to rot in place.

Reading the Crust

Get down to the wood and use a lens. The individual tiles, often called frustules, are usually one to three millimetres across and slightly polygonal, packed together like paving. Each one is flat-topped or very slightly convex, with a distinctly raised, sharp edge. The cracks between them are dark, sometimes almost black where dirt has collected, and they run right down through the crust to the timber, so the plates really are separate islands rather than a continuous sheet with surface fissures.

Colour depends on age and weather. Actively growing patches are cream, ivory or very pale buff, sometimes with a faint pinkish or ochre wash. Old, weathered patches bleach to pale grey and lose contrast against the wood. The advancing margin, where the fungus is colonising fresh timber, is often a narrow unbroken zone of paler, smoother crust that has not yet cracked, and it can be slightly downy.

A single colony can be a few centimetres across or can carpet an entire trunk face for a metre or more, several separate patches running together into one continuous mosaic.

The Fertile Surface

The spore-bearing layer is simply the flat upper face of each tile. There are no gills, no pores, no teeth and no spines - this is a smooth-hymenium crust fungus, and the whole exposed surface is fertile. Under a lens the tile tops look matt and finely powdery rather than waxy or shiny.

Texture is a key confirmation. Try to lift an edge with a knife point. Stereum crusts, the usual confusion, are leathery and will peel away in a flexible sheet, often bringing a strip of bark with them. Ceramic Parchment is bone-hard and firmly cemented to the wood; it fractures and chips rather than peeling, and dry material shatters into fragments.

Section, Tissue and Colour Change

Chisel a small piece off with the wood attached and look at a vertical cut. The crust is typically one to three millimetres thick, sometimes more in old colonies, and shows faint layering, because the fungus is perennial and adds a new fertile surface over the old one in successive seasons. The tissue is pale, whitish-buff to cream, dense and woody. It does not soften noticeably when wetted, though the fertile surface can look a little brighter.

There is no colour change on cutting: no reddening, no bruising, no latex, no juice. That absence matters, because several of the leathery crusts you might mistake it for - the bleeding Stereum species in particular - release a red juice or stain red where scratched when fresh.

Taking a Spore Print

Crusts are awkward to print, but it can be done and the result is worth having. Choose a fresh, actively growing patch during damp weather, chip off a piece of wood carrying the crust, and suspend or prop it fertile-side down a few millimetres above a piece of dark card inside a closed box with a damp tissue for humidity. Leave it overnight in a cool place. The deposit is white, and against black card even a thin dusting is obvious. Dry, weathered, grey material will usually give nothing at all, so timing is everything.

Substrate, Rot Type and Season

The substrate is close to diagnostic. Ceramic Parchment is an oak specialist, and it wants hard, decorticated, well-seasoned heartwood rather than sappy fresh timber or bark-covered branches. Old stumps, big fallen trunks, sawn ends, worked oak in the open - these are the places to look. Records from other hardwoods exist but are rare enough that a tessellated crust on oak is the sound assumption.

Break a piece of the underlying wood open and look at the rot. This species causes a white pocket rot: the timber develops small elongated white or cream lens-shaped pockets, aligned with the grain and separated by firm, still-brown wood, giving a honeycombed, tunnelled appearance without any insect galleries. Finding that pocketing under a tiled crust is an excellent confirmation.

Being perennial and hard, the fungus is present in every month of the year. Fresh growth and sporulation are best in autumn and in mild damp spells, but the mosaic itself never disappears.

Separating the Look-alikes

Xylobolus subpileatus grows on the same oak wood and has the same hard texture, but it builds thick shelving brackets with a dark, coarsely hairy to crusty upper surface, and its fertile underside stays more or less continuous rather than dividing into a field of small tiles.

Stereum species (S. hirsutum, S. gausapatum, S. ostrea, S. rugosum) are the commonest confusion. They are thin and leathery-flexible, peel easily, usually turn up at the edge into a small bracket with a hairy or concentrically zoned upper surface, and are often yellow, ochre or greyish. Cracking, where it happens, is irregular and coarse, never a neat tile pattern. Several stain red when scratched fresh.

Peniophora and Aleurodiscus species are thin, waxy or gelatinous, frequently pink, lilac or grey, and typically colonise attached branches with bark rather than exposed heartwood. Their cracking is shallow and irregular.

Vuilleminia comedens is waxy and glassy, forms on attached oak twigs and rolls the bark back off the wood - a completely different texture.

Resupinate polypores flatten themselves on dead oak too, but a lens instantly shows pores rather than a smooth fertile face.

Crustose lichens on the same sun-bleached timber can also crack into plates, but they are usually grey-green or greenish, have a granular or scurfy surface with disc-shaped fruiting bodies, and never yield a white spore deposit.

Working Checklist

Hard, non-peeling crust; cream to pale grey; broken into a mosaic of small polygonal tiles with dark cracks; smooth fertile surface; no colour change; white spore deposit; on bare decorticated oak heartwood; white pocket rot in the wood beneath; present all year. Tick those and there is nothing else it can reasonably be.