Bleeding Conifer Crust

Stereum sanguinolentum is the conifer counterpart of the bleeding broadleaf crusts, and one of the most abundant fungi of managed spruce and pine forest. It spreads as a thin, closely attached sheet over barkless conifer wood, with the outer margin lifting into a narrow, wavy, silky-hairy shelf seldom more than a centimetre deep.

Colours are subdued: pale grey, greyish buff, silvery or pale ochre-brown on the upper reflexed surface, with a smoother greyish to violet-tinged fertile side. The species announces itself by the red droplets that well up along a scratch on fresh material, a reaction it shares with S. rugosum and S. gausapatum but which no other common conifer crust shows.

Beyond the field, this fungus is significant in forestry as a coloniser of wounds on living conifers, entering through pruning cuts, extraction damage and broken branches. Its role in both standing and fallen conifers makes it one of the most frequently encountered Stereum species across the boreal and montane forests of the Northern Hemisphere.

Fruit body

Effused to effused-reflexed, forming thin sheets that may cover large areas of a log, with reflexed margins 3–15 mm deep. The turned-out portion is thin, flexible and often strongly wavy or lobed, and adjacent shelves fuse into a continuous ruffled fringe running along the wood.

Upper and fertile surfaces

The upper side of the reflexed part is finely silky-hairy to felted, greyish, buff or ochre-brown, sometimes faintly zoned, and turns algal-green when weathered. The fertile surface is smooth and unbroken — no pores, teeth or folds — in shades of pale grey, greyish buff, or with a faint violet or lilac tint when fresh.

Bleeding reaction

A scratch on a fresh, moist fertile surface produces prompt red droplets that spread along the line. This is the key field test and works only on hydrated material.

Flesh and spore print

Flesh is very thin, tough and leathery, under a millimetre thick, drying hard and brittle. The spore deposit is white; spores are small, smooth and cylindric-ellipsoid, amyloid.

The fungus is restricted to conifer wood — spruce, pine, fir, larch and Douglas fir — appearing on fallen trunks, cut stumps, stacked logs, dead attached branches, and the exposed wood of wounds on living trees. It is particularly abundant in plantation forest and on freshly cut timber.

It persists as dried crusts throughout the year, with fresh growth and reliable bleeding from autumn through winter into spring. Distribution is circumboreal, spanning the conifer forests of Europe, northern Asia and North America.

Stereum sanguinolentum causes a white rot in conifer sapwood and heartwood. It is chiefly a saprotroph on dead wood, but it is also a well known wound coloniser of living conifers, entering through bark injuries and pruning scars and then decaying the wood behind the wound while the tree continues to grow around it.

The fungus is also an early coloniser of cut stumps, establishing on freshly exposed surfaces within weeks. It is the exclusive host of the jelly fungus Tremella encephala, which parasitises its mycelium in the wood and fruits alongside it as pink brain-like cushions with a firm white core, so the presence of that jelly is a reliable indicator that this crust is present.

Amylostereum areolatum and Amylostereum chailletii are the closest conifer look-alikes, forming similar thin greyish to brownish crusts with reflexed edges, but neither releases red juice when scratched; their fertile surfaces also tend to be more distinctly brown and cracked. Stereum rugosum bleeds identically but is much thicker, paler and largely resupinate, and grows on broadleaf wood.

Chondrostereum purpureum has a smooth fertile surface in clear purple to lilac tones with a white hairy reflexed edge and gives no red reaction. Thin resupinate polypores such as Trichaptum abietinum occur on the same conifer logs and can look superficially similar from above, but they have a violet, toothed to poroid fertile surface rather than a smooth one.