Split Porecrust Identification Guide

Finding It in the First Place

Split Porecrust rewards the habit of turning branches over. It grows as a flat crust pressed directly against dead wood, almost always on the underside or the shaded face where humidity lingers, so it is invisible until you lift or roll the branch. The productive substrates are fallen and still-attached dead hardwood branches of oak, hazel, birch, willow, ash and beech, plus old fence rails and neglected cut timber. Patches begin as small pale spots and spread outward, often merging until a strip of crust runs 10 to 30 cm or more along the branch. First impression is of a thin cream to buff coating, dry, tightly adherent, with a slightly fuzzy paler edge, and a surface that is not smooth but broken into an irregular texture that repays a lens.

Reading the Surface

This is where the species earns its name. On a young or vertical-facing patch the fertile surface is poroid: small angular pores, roughly two to four per millimetre, arranged in an untidy honeycomb. Follow the same crust to an older area or to a downward-facing part of the branch and the pores begin to break down. Their walls tear, the dividing tissue splits and lengthens, and the surface converts progressively into flattened, jagged, tooth-like plates and irregular spines. Mycologists call this an irpicoid surface, and Split Porecrust often shows the entire sequence, tidy pores through split pores to ragged teeth, on a single specimen. That variability is exactly what the name paradoxus records, and a crust that presents two apparently different surfaces at either end is a strong pointer.

Colour runs from white when very fresh through cream to pale ochre-buff, sometimes drying a slightly darker tan. It does not develop bright yellow, orange, pink or grey tones. There is no zonation, no varnish and no colour change where you scratch it.

Reading the Margin

Always examine the edge of the patch with a lens. In Split Porecrust the margin is thin, paler than the fertile centre, and finely fibrillose to cottony, fading gradually into the wood rather than ending in an abrupt raised rim. In damp conditions fine white mycelial threads may run out from the margin across the bark. On horizontal branch undersides the crust occasionally forms a narrow turned-out shelf at the top edge, but it is never a proper bracket with a defined hairy or zoned upper surface.

Texture, Section and Colour Change

Press the crust with a fingernail. Fresh material is tough and slightly leathery to corky, firmly attached, and it cannot be peeled off in one sheet; dried material becomes hard and brittle and may crack away in flakes. Cut a section down through the crust with a razor and you will find a very thin layer, typically well under 2 mm thick including the projecting teeth, with a thin white subiculum of hyphae between the fertile layer and the wood. There is no distinct fleshy context, no separate tube layer as you would see in a bracket, and no colour change on cutting or bruising. The odour is negligible.

The Spore Question

Crust fungi are awkward to print but it is worth doing at least once. Cut a piece of colonised branch, prop it fertile-face down over black paper in a covered box with a damp tissue for humidity, and leave it overnight or longer. The deposit is white and usually thin. A microscope adds far more here than for a gilled mushroom: the spores are small, smooth, thin-walled and broadly elliptical, the hyphal system is monomitic with clamp connections, and the hymenium carries distinctive swollen, capitate cystidia. In a genus where field characters overlap, those microscopic features are what a specialist will use to finalise the name.

Substrate, Season and Ecology

Split Porecrust is a wood-decay fungus of dead broadleaved wood, causing a white rot in which lignin is broken down and the residual wood becomes pale, soft and fibrous. It works on attached dead branches high in the crown as readily as on fallen material on the ground, which is why storm debris often arrives already colonised. It is common, widespread and effectively perennial: fruit bodies persist through the year, resume growth in mild damp weather and can be found in every month, though they are freshest and palest in autumn and winter. Because it tolerates a range of hosts and situations, it is one of the crusts most likely to turn up on any given hardwood branch you inspect.

Separating the Look-alikes

The closest relative, Schizopora flavipora, keeps a regular poroid surface far longer, has smaller pores at roughly four to six per millimetre, tends toward a warmer ochre-yellow tone, and is more frequently found on conifer wood and in warmer regions. It rarely develops the ragged tooth-like breakdown that characterises Split Porecrust.

Xylodon radula begins as scattered separate tubercles or warts on the wood that later fuse into a poroid crust, its pores are on average larger and more open, and its margin is whiter and more distinctly fringed.

Milk-white toothed polypore, Irpex lacteus, is the most likely field confusion. It is whiter and more sharply toothed from the outset, its teeth are longer and flatter, its texture is tougher, and it very often forms a narrow reflexed bracket edge with a finely hairy upper surface, whereas Split Porecrust is usually flat and buff-toned with pores still visible somewhere on the patch.

Steccherinum ochraceum is toothed but distinctly ochre to salmon-pink with a conspicuous fibrillose margin, and Junghuhnia species run to orange-tan.

Resupinate forms of Trametes and Antrodia are thicker and more rigid, with a well-defined tube layer that can be seen in section as a discrete band, and their pores remain regular.

Purely toothed crusts in Hyphodontia and related genera never show a poroid stage at all, and the wrinkled orange crusts of Phlebia are separated by colour and by the complete absence of pores or teeth.

Field Checklist

Thin cream to buff crust tightly attached to dead hardwood; surface poroid in places and torn into jagged flattened teeth elsewhere on the same specimen; pores roughly two to four per millimetre where intact; paler finely fibrillose margin; tough when fresh and hard when dry; no colour change; white spores; present all year. Where field characters run out, the capitate cystidia and clamped monomitic hyphae settle it under the microscope.