Bleeding Oak Crust | Stereum gausapatum Identification Guide

The Habitat Picture

Start with oak. This species is so strongly tied to Quercus that the tree itself does half the identification for you, and the typical find is in old oak woodland, wood pasture, a hedgerow with standard oaks, or a coppice with sweet chestnut mixed in. Look at dead branches still attached to a living tree, at the brash left after felling, at fallen limbs bedded into the leaf litter, and at the split faces of old stumps. What you will see is a brown, wavy encrustation running along the wood, its outer edge lifted into rows of small shaggy shelves, often stacked one above another in tiers on a vertical face. Where the wood is horizontal, the whole thing may lie flat as a skin with only a thin fringe raised. On a still, wet December morning the colony feels supple and slightly rubbery; in high summer it is a hard, pale, curled crust that looks half dead.

Growth Form and Size

The habit is effused-reflexed with a strong bias toward the effused, that is, toward the flat crust. Patches begin as small ovals a couple of centimetres across, then spread and merge into strips that can run for 30 cm or more along a branch. The reflexed shelves are narrow, usually 0.5 to 1.5 cm projecting, with irregular, lobed and often deeply wavy margins that give the fungus a torn, frilly outline. Thickness is around a millimetre. Note how firmly the flat part grips the wood: it is not peelable in one piece the way a young bracket sometimes is, and trying to lift it takes fibres of wood with it.

The Upper Surface

On the reflexed portion, the sterile upper surface is conspicuously hairy. That shagginess is what the species name refers to, and it is coarser and more felted than in many of its relatives, especially near the point of attachment. Colour is ochre-brown to grey-brown with faint concentric zoning, becoming grey and matted with algae in older tissue. The extreme growing margin is paler, cream to ochre, and slightly velvety. Because the hairs trap water, a fresh specimen looks darker and more richly brown after rain and considerably paler when dry.

The Fertile Surface and the Scratch Test

Underneath, or across the whole face on a purely flat patch, the fertile surface is smooth. It has no pores, no gills, no spines: just an even skin, sometimes gently uneven or tuberculate, and often minutely cracked in old material. Colour is where this species scores over its relatives. It is typically a warm ochre-brown, tan or reddish-brown, sometimes with a greyish or faintly lilac cast, and rarely as pale or as grey as its conifer counterpart.

Then do the scratch. Draw a fingernail, knife tip or twig across a fresh, moist fertile surface and watch. Within seconds, a clear red to blood-red line appears along the scratch, sometimes spreading a little to either side. It marks the track precisely rather than forming free droplets, because the colour comes from pigmented vessel hyphae in the fertile layer that rupture when torn rather than from a true latex. Only well-hydrated material reacts. A crust that has been sitting in sunshine, or one collected in a dry frost, may refuse entirely, in which case rehydrate it in wet moss or damp paper for half an hour and try again on an untouched area.

Flesh, Section and Texture

Slice a shelf vertically with a razor blade. You are cutting through less than a millimetre of tissue, and under a lens you can see a hairy top layer, a thin dark cortical line beneath it, and the fertile layer below that. The consistency is leathery when moist and horn-hard when dry, and dried material revives fully when wetted, which is why old collections can still be scratch-tested. There is no fleshy interior, no stem and no separable pore layer.

Spore Print and Microscopic Confirmation

Cut off a well-reflexed piece with a fragment of wood and set it fertile-side-down over a glass slide inside a sealed box with wet tissue. Left overnight in the cool, it deposits a white and usually rather scanty print, best seen against dark card in raking light. The spores are smooth, cylindrical to narrowly ellipsoid and slightly curved, and they stain blue-grey in Melzer's iodine. That amyloid reaction, together with the smooth fertile surface, places the collection firmly in the group and separates it from various resupinate fungi that superficially resemble it.

Substrate, Season and Ecology

Substrate is the single most useful character. Oak dominates, with sweet chestnut a regular alternative and occasional records on other broadleaf trees. It occupies dead attached branches, recently fallen limbs, felling brash, stumps and the exposed heartwood of veteran trees, and it is also known as a wound coloniser of living oaks, entering through broken branch stubs and causing a pipe rot in the heartwood. Fruit bodies are present all year and persist for many months, but they are only worth testing between autumn and spring when the wood stays wet. Attached, still-suspended branches often produce better formed shelves than logs on the ground, because the fungus is not smothered by litter and moss.

Telling It From the Other Bleeding Crusts

This is the part that needs discipline, because three species bleed and they are separated mainly by substrate and habit.

• Bleeding Conifer Crust, Stereum sanguinolentum, bleeds identically, but it grows on spruce, pine, fir and larch. Its fertile face is paler and greyer, and its shelves are typically thinner and more regularly zoned. If the wood is coniferous, the identification changes.
• Bleeding Broadleaf Crust, Stereum rugosum, also bleeds and also uses broadleaf wood, especially hazel, birch and oak. It forms a thick, hard, almost entirely flat crust with little or no shelf, and its surface is knobbly and uneven rather than shaggy-edged. Where gausapatum makes tiered frilly rows, rugosum makes a lumpy pavement.
• Hairy Curtain Crust, Stereum hirsutum, shares oak but never bleeds. Its fertile surface is a bright yellow to orange-buff, far more vivid than the muted brown of the bleeding species, and its shelves are better developed and more boldly zoned.
• Yellowing Curtain Crust, Stereum subtomentosum, forms larger, thicker fans on willow and alder in wet places and stains yellow, never red, when scratched.
• Xylobolus frustulatus grows on the dry, exposed heartwood of very old oak and breaks into small, hard, whitish tiles separated by cracks, with no shelves and no bleeding.
• Chondrostereum purpureum has a purple to lilac fertile face and gives no red reaction.

Working Sequence in the Field

Identify the tree as oak or sweet chestnut. Confirm a thin crust with narrow, shaggy, wavy reflexed edges, often tiered. Confirm the fertile surface is smooth and warm brown. Scratch fresh material and look for the red line within seconds. If all four agree, you can name it confidently on the spot, with a spore print and an iodine test available as backup.