Ceramic Parchment

Appearance

The fruit body, or crust, of ''Xylobolus frustulatus'' has a woody texture and is perennial. It is mostly 1–2 mm thick, although it can be considerably thicker. The crust is ''frustose'' , and infrequently curled at the edges. The upper surface is zonate , and more or less smooth. The hymenial surface is smooth to the naked eye, although long soft hairs can be seen when viewed with a microscope. These 'hairs' are protruding acanthocystidia and hyphae. Young layers are pale ochraceous, while older ones dull to deep brown. The fungus is inedible, and lacks any distinctive taste or odor.

The hyphal system is monomitic, meaning that there are only generative hyphae are present. These vertically arranged, short-celled hyphae form transitions to acanthocystidia, and have a diameter of about 3.5–5 μm. They are sparsely branched, and hyaline to yellowish-brown, although those in older layers may be more strongly pigmented. Other hyphae are few or absent, although they can be most readily observed in very thin sections. Measuring 3–5 μm wide, they are vertically arranged, thin to moderately thick-walled, and form transitions to pseudocystidia. All of the hyphae of ''X. frustulatus'' lack clamp connections.

Pseudocystidia are rare. Thin to moderately thick-walled, they rarely project above the basidia and acanthocystidia. The acanthocystidia are numerous, and have dimensions of 25–30 μm long by 4–5 μm wide. The basidia are shaped like long clubs, four-spored, and measure 25–30 by 4–5 μm. They are smooth or have a few basal protuberances . The spores are short-ellipsoid in shape, thin-walled or with a slight wall thickening, smooth, typically measuring 4.5–5 by 3–3.2 μm. They have a distinct amyloid reaction.

Naming

''Xylobolus frustulatus'' is readily identified in the field because of its distinctive strongly cracked fruit bodies. ''Laxitextum bicolor'', commonly known as the "two-tone parchment", is a potential lookalike. It forms a crust-like, spreading patch of spongy, pliant overlapping caps on rotting deciduous wood, particularly alder. It has a brownish upper surface with a suede-like texture, a white lower surface, and curled edges that give it a shell-like appearance.

Habitat

The fungus is saprobic, and grows only on well-rotted wood of oak. It occurs on branches and trunks lying on the ground, and is more rarely seen on branches that are still attached to the tree. Found in northern Europe, and North America, it has also been recorded from Asia, including Japan and Taiwan. In terms of the classification of white rot fungi, ''X. frustulatus'' is a ''selective degrader'', meaning that it breaks down lignin and hemicellulose faster than cellulose. The fungus is one of several known to break down timbers used in coal mines.

Sporulation generally takes place during the summer, as most specimens from autumn and early spring are sterile with the hymenium consisting only of acanthocystidia. ''Xylobolus frustulatus'' may be parasitized by the ''Hypomyces'' mold ''H. xyloboli''.