Bleeding Broadleaf Crust

Stereum rugosum is the flattest of the common bleeding crusts. Where its relatives raise obvious little brackets, this species stays largely resupinate, spreading as a thick pale sheet over the surface of dead branches and only lifting a narrow rim at the edges. Colonies can run for tens of centimetres, coalescing into an almost continuous pale skin on a hazel stem.

The genus Stereum has a smooth fertile surface with no pores, teeth or wrinkled folds, and several of its species share a striking property: fresh tissue exudes red droplets when damaged. That reaction is a pigment response, not a wound in the animal sense, and it fades within a day or two of the fruit body drying out.

Among the bleeders, S. rugosum is recognised by its thickness — often 1–2 mm, noticeably fleshier than its relatives — its pale buff to greyish cream colour, and its strong association with hazel and other broadleaf shrubs and trees across Europe and temperate Asia and North America.

Fruit body

Mostly resupinate, forming thick sheets 0.5–2 mm deep that spread over the substrate for many centimetres and coalesce. The margin is usually tightly adnate and slightly paler, occasionally lifting into a narrow reflexed lip only a few millimetres wide; a full bracket is rarely developed.

Surface

The fertile surface is smooth to shallowly lumpy or undulating, without pores, teeth or radial wrinkles, and matt rather than glossy. Colour is pale buff, cream, greyish ochre or faintly pinkish, darkening to ochre-brown or greyish with age. Old crusts commonly crack into small plates as they dry.

Bleeding reaction

Scratching or cutting a fresh, moist crust produces bright red to blood-red droplets along the damage line within seconds. The reaction is strongest in autumn and winter on well-hydrated material and is absent in old, dried specimens.

Flesh and spore print

Flesh is tough, dense and leathery, pale within, drying hard and horny. There is no stalk, ring or volva of any kind. The spore deposit is white; spores are smooth and ellipsoid to cylindric.

This species fruits on dead broadleaf wood, showing a particular affinity for hazel, and also occurring commonly on birch, oak, alder, beech and ash. It typically colonises dead branches that are still attached to a living shrub or tree, as well as recently fallen brash and coppice stools.

It is present year-round as a persistent crust, with fresh, strongly bleeding growth from autumn into winter. The species is common throughout temperate Europe and recorded across northern Asia and North America; in hazel coppice it can be the dominant crust fungus on dead stems.

Stereum rugosum is a saprotroph causing a white rot, and it also behaves as an early coloniser of branches that die back while still attached, entering through wounds and dying twigs before the branch falls. Decayed wood becomes pale, soft and fibrous as lignin is removed.

The crust is effectively long-lived, adding new fertile layers over old and persisting on the same stem for several seasons. Because its mycelium is already inside a branch before that branch reaches the ground, it usually has a head start over other decay fungi, which is one reason it dominates dead hazel and birch stems so thoroughly.

Stereum gausapatum also bleeds but is thinner, more clearly reflexed at the edges into small hairy tan brackets, and is strongly associated with oak. Stereum sanguinolentum likewise bleeds but is thinner still, greyer, has a distinctly fringed wavy edge, and grows on conifer wood rather than broadleaf.

Non-bleeding relatives are separated by the scratch test: Stereum hirsutum is more brightly yellow-orange with a hairy upper surface, and Stereum subtomentosum stains yellow rather than red. Among unrelated crusts, Peniophora species are thinner, more pinkish or lilac, and often form small separate patches with rolled edges when dry, while Chondrostereum purpureum has a violet fertile surface and a white hairy reflexed edge and does not release red juice.