Bleeding Conifer Crust | Stereum sanguinolentum Identification Guide

The Setting You Will Be Standing In

Almost every encounter with this fungus starts in conifer wood rather than broadleaf wood. Picture a spruce plantation after a gale, a stack of pine logs at a forest ride, a wind-snapped fir lying with its branches still attached, or a row of stumps left from thinning. Turn a fallen branch over and the underside is often skinned with a wavy, greyish-buff sheet, its free edge lifted a centimetre or two clear of the bark like the brim of a hat. Individual pieces are small, but they run together into ribbons that can stretch the length of an arm along a log. In wet weather the whole colony is soft and pliable and slightly translucent at the margin; in a dry spell it shrinks, curls upward and turns hard and pale, and the edges look almost bleached.

Deciding on the Growth Form

The technical description is effused-reflexed, and the fungus really does sit halfway between two habits. Part of it is a resupinate crust glued flat to the wood, and part of it peels away as a shelf. Which half dominates depends on where the wood sits. On the underside of a horizontal log you get mostly crust with a narrow reflexed lip; on a vertical cut face or a standing stump you get proper little brackets, fan-shaped or shell-shaped, 0.5 to 3 cm out from the wood and rarely more than 1 to 2 mm thick. Neighbouring shelves fuse side to side into scalloped rows and tiers. Always note this dual habit, because several of the crusts it is confused with are one thing or the other but not both.

Reading the Upper Surface

Get a hand lens onto the sterile top of a reflexed piece. When young and growing it is finely hairy or velvety, with matted hairs lying in the direction of growth, and the colour is a muted grey-buff to ochre-brown organised into faint concentric zones. The bands are subtle rather than the bold tiger-stripes of a turkeytail. Older parts weather: the hairs wear away, the surface goes grey and smooth, and green algae often colonise the oldest tissue near the point of attachment. The growing margin is the freshest part and is typically cream to almost white, thin, and slightly downy. If your specimen is uniformly grey, felted and dead-looking all over, you are probably looking at last season's tissue, and every reaction test below will be unreliable.

The Fertile Surface and the Bleeding Reaction

Flip the shelf. The fertile face is smooth. There are no gills, no pores, no teeth, nothing but a slightly uneven skin with low bumps and occasional shallow wrinkles. Its colour is pale grey-buff, tan, or faintly lilac-tinged, usually paler than the top. This smoothness alone rules out a large slice of the wood-decay fungi you might otherwise consider.

Now do the test the species is named for. Take a knife point, a thumbnail or a twig and draw a single firm line across the fertile surface of a fresh, moist specimen. Within a few seconds to a minute, a distinct red to reddish-brown line develops exactly where you scratched. It stays as a line rather than welling into droplets, because there is no true latex here; the pigment comes from thin-walled vessel hyphae in the fertile layer that release their contents when torn. Damp, actively growing material bleeds hard and fast. Sun-dried, frozen or over-mature material may not react at all, which is the single commonest reason people reject a correct identification. If nothing happens, wrap the piece in wet moss or damp tissue for twenty to thirty minutes and repeat on an untouched patch.

Flesh, Section and Texture

Cut a clean vertical slice with a razor blade and look at it side-on with a lens. The whole structure is astonishingly thin, well under a millimetre in most places, and consists of a hairy top layer, a thin darker line beneath it, and the fertile layer below. Texture is leathery and flexible when moist, rigid and brittle when dry, and it revives on wetting, which is why dried herbarium material can be tested again years later. There is no soft, fleshy interior to speak of, and no distinct stem or point of attachment beyond a broad fused base.

Taking a Spore Print

This is fiddly but worth doing once. Cut away a well-reflexed piece with a scrap of wood attached, then rest it fertile-side-down over a glass slide or a strip of dark card, inside a closed box with a wet tissue for humidity. Leave it overnight in a cool place. The deposit is white to whitish and often very sparse, so a dark background and a raking light help. Under a microscope the spores are smooth, cylindrical to narrowly ellipsoid and sausage-shaped, and they turn blue-grey in Melzer's iodine, an amyloid reaction shared with its relatives.

Substrate, Season and Ecology

Substrate is nearly diagnostic. This fungus is a conifer specialist, most often on Norway spruce, but also pine, silver fir, larch and Douglas fir. It takes dead attached branches, fallen trunks, cut stumps and stacked timber, and it is also a well-known wound coloniser of living conifers, entering through extraction scars, broken branch stubs and pruning cuts and staining the heartwood. Fruit bodies persist through the year, but they are at their most convincing from autumn through to early spring when the wood is soaked, and that is also when the bleeding reaction is at its sharpest.

Separating the Look-alikes on Morphology

The crust genus splits neatly if you take substrate first, then the scratch test, then texture.

• Hairy Curtain Crust, Stereum hirsutum, is the default hardwood species. It has a coarsely hairy, brighter yellow-buff to orange top, a vivid yellow-orange fertile surface, and it does not bleed at all.
• Bleeding Oak Crust, Stereum gausapatum, bleeds just as readily but grows on oak and sweet chestnut, is shaggier, redder-brown on the fertile face, and tends to form long tiered rows on standing dead branches.
• Bleeding Broadleaf Crust, Stereum rugosum, bleeds too, but forms a thick, hard, almost entirely flat crust with only the narrowest reflexed edge, mostly on hazel, birch and oak.
• Yellowing Curtain Crust, Stereum subtomentosum, is a thicker, better-formed fan on willow and alder in wet ground; scratching turns it yellow, never red.
• Amylostereum chailletii and Amylostereum areolatum share conifer wood and a grey-brown look but never bleed; areolatum is harder and its surface cracks into small plates.
• Chondrostereum purpureum has a distinctly lilac to purple fertile surface and no red reaction.
• Trichaptum abietinum grows abundantly on the same conifer logs, but its underside is violet-tinged and breaks up into pores and flattened teeth rather than staying smooth.

A Quick Field Routine

Confirm conifer wood. Confirm a thin crust with a reflexed, faintly zoned, finely hairy edge. Confirm a smooth, gill-free, pore-free fertile face. Scratch fresh material and wait for the red line. If all four hold, the identification is secure without a microscope.