Hairy Curtain Crust

The Hairy Curtain Crust (Stereum hirsutum) is among the most abundant wood-decay fungi of temperate broadleaved woodland, and on many oak and beech logs it forms the dominant covering. It belongs to the Stereaceae, a family of fungi whose spore-bearing surface is completely smooth rather than divided into gills, pores or teeth, and which produce thin, leathery, crust-like or shelving fruit bodies.

Fruit bodies typically start as a flat crust spreading over the wood and then turn outward and upward at the edge, producing wavy shelves that are hairy and zoned above and smooth and brightly coloured below. This effused-reflexed growth form, and the way ranks of brackets fuse into long undulating curtains along a fallen branch, is the origin of the English name.

Because it is tough and weather resistant, it can be found in every month of the year, and its bright orange-yellow underside gives welcome colour to winter woodland when almost nothing else is fruiting.

Fruiting body

Thin, tough and leathery, individual brackets 1-4 cm across and under 2 mm thick, semicircular to fan-shaped or irregularly wavy, usually fused laterally into long tiers or curtains and often partly spread flat over the wood surface. The upper surface is densely covered with short stiff hairs, giving a felty or bristly feel, and is concentrically zoned in bands of grey, buff, ochre and yellow-brown; algae frequently colonise old specimens and turn them green.

Fertile surface

The underside is completely smooth: no pores, no gills, no teeth, no wrinkles beyond gentle undulations. It is bright yellow-orange to warm ochre when fresh and moist, fading to dull buff, tan or greyish with age and dryness. This bright smooth underside is the single most useful character. Critically, it does not exude any coloured liquid when cut or scratched.

Flesh and spore print

The flesh is very thin, tough, pliable when damp and hard and brittle when dry, pale buff to yellowish, with an internal structure of two layers separated by a thin dark line in some specimens. The spore print is white, though it is difficult to obtain from such a thin fruit body.

The Hairy Curtain Crust fruits on dead hardwood of almost every kind, with oak the most characteristic host, followed by beech, birch, hazel, ash and many others. It occurs on fallen branches, standing dead limbs, stumps, cut log ends, timber stacks and even worked wood in damp conditions, and it is one of the first fungi to appear on freshly cut hardwood surfaces. Records on conifer wood are uncommon.

It is essentially cosmopolitan in temperate regions, abundant throughout Europe, North America and Asia. Fruit bodies are produced year round and persist for many months, so the species can be recorded in any season; the brightest colours appear in wet weather from autumn through spring.

Stereum hirsutum is a white-rot saprotroph and a pioneer coloniser of freshly exposed hardwood. Its spores land on cut surfaces and wounds within days, and the mycelium establishes rapidly, degrading lignin and cellulose and eventually leaving the wood pale and soft.

It is a model organism for the study of fungal competition. Where two genetically distinct colonies of the species meet inside a log, they form a dark demarcation barrier, and these interaction zones produce the black lines familiar in spalted wood. The species is also frequently attacked by other fungi in turn, notably the jelly fungus Tremella aurantia and, on conifer-inhabiting relatives, other Tremella species, which parasitise the Stereum mycelium and fruit directly on its brackets. This makes it an important node in the community of decaying wood, supporting parasitic fungi as well as bark-lice, mites and beetle larvae.

The False Turkey Tail (Stereum ostrea) is closely related but has a much smoother, less hairy cap with broader, more strongly contrasting concentric zones in rich orange, brown and buff, and it forms larger, more regularly fan-shaped brackets. Stereum complicatum is smaller, forms tightly fused rows along oak twigs, and has a more uniformly cinnamon-orange underside.

Stereum sanguinolentum and Stereum rugosum are the crucial separations for anyone confirming an identification: both exude a red juice when the fresh fertile surface is scratched, while Stereum hirsutum never does. Stereum sanguinolentum also grows on conifer wood and has a much less hairy, paler cap.

Turkey Tail (Trametes versicolor) is easily distinguished by turning the bracket over: it has a white surface densely covered in fine round pores, whereas all Stereum species have a completely smooth underside. The Silverleaf Fungus (Chondrostereum purpureum) has a similar shelving habit but its smooth fertile surface is lilac to purple-brown rather than orange-yellow.