Ceramic Parchment

Ceramic Parchment is one of the most instantly recognisable resupinate fungi in temperate woodland. Rather than forming a smooth sheet, the fruiting layer fractures as it grows into hundreds of small angular blocks, each one to three millimetres across, separated by narrow dark fissures. The overall effect on a weathered oak log is a pale tessellated pavement, which is the origin of both the English name and the scientific epithet frustulatus ("broken into small pieces").

The genus Xylobolus sits in the Stereaceae, the same family as the familiar Stereum crusts, but its members are far harder and more persistent. Xylobolus frustulatus is a perennial: a single colony may occupy the same piece of oak heartwood for decades, adding new fertile tissue each season and slowly extending across the exposed surface.

Because it needs bark-free, well-seasoned oak, this species is strongly associated with old woodland, wood pasture and long-undisturbed stumps. Its presence is often taken as an indicator of continuity of dead oak wood in a site.

Fruiting body

Entirely resupinate (flat against the wood) with no cap or stalk, spreading in irregular patches that may cover many tens of centimetres. The fertile surface is cream, buff or pale grey, sometimes with a faint pinkish tone when very fresh, and is divided into small angular tiles by black or dark grey cracks.

Surface and texture

The tiles are hard, brittle and firmly cemented to the wood; they cannot be peeled away intact and tend to chip. The hymenium itself is smooth, without pores, teeth or wrinkles. Growing margins are thin and slightly paler, often outlined by a dark line where the crust is advancing across bare wood.

Flesh and spore print

Flesh is extremely thin and hard, pale within, and does not change colour when cut. The spore deposit is white, though it is rarely observed in the field on such a tightly appressed fungus.

Found almost exclusively on oak (Quercus), and specifically on hard, decorticated heartwood — the smooth bare surfaces of old stumps, fallen trunks and cut ends that have long since shed their bark. It favours wood that is dry and exposed rather than sodden, and often occupies the upper faces of large logs in open woodland, parkland and wood pasture.

Fruiting bodies are perennial and can be found in any month; new growth is added in damp periods. The species is widespread across the north temperate zone, including Europe, and is generally most frequent in regions with a long history of oak woodland.

Xylobolus frustulatus is a saprotroph responsible for a distinctive white pocket rot of oak heartwood, in which the decayed wood becomes riddled with small elongated white pockets separated by firmer tissue. This slow, selective decay is a significant recycler of the dense, durable heartwood that many other fungi colonise only with difficulty.

Colonisation typically begins in wood that is already partly decayed and has lost its bark, and the fungus then persists for many years, laying down successive fertile layers. Spores are produced from the smooth tile surfaces and dispersed by air currents to fresh exposures of bare oak.

The tessellated, tile-like cracking is close to unique among crust fungi, but weathered Stereum species can suggest it at a glance. Stereum rugosum and Stereum gausapatum form thicker, smoother crusts that often turn out a narrow bracket-like edge and do not break into regular blocks. Vuilleminia comedens is waxy and translucent and characteristically rolls the bark back on oak branches rather than sitting on bare heartwood.

Peniophora quercina also grows on oak but is lilac-grey, thin and flexible, curling away in flakes when dry. Its close relative Xylobolus subpileatus produces genuinely bracket-like reflexed edges with a dark, velvety upper surface and does not form the fine mosaic of small tiles.