Hairy Curtain Crust Identification Guide

First Impression and Setting

Hairy Curtain Crust is one of the few fungi you can look for on any day of the year. The scene is a fallen oak or beech limb, a stack of cut logs, a stump in a hedge or a wind-snapped branch still hanging in the canopy. What draws the eye is colour: bright egg-yolk yellow to orange edging along the rim of a dense, tiered, wavy crust that has spread along the wood in rows.

Step closer and the structure resolves. There are no gills and no obvious pores. The fungus forms a thin, leathery skin over the wood whose upper margin peels away into small overlapping brackets, so that a single branch can carry a continuous frilly curtain a metre long. On the underside of a log the same fungus may stay entirely flat, a crust with no brackets at all. That combination of flat crust and lifted bracket is called effused-reflexed, and recognising it is the first step.

Reading the Upper Surface

Individual brackets are 1 to 4 cm across, occasionally more, and only about a millimetre thick. They are semicircular to fan-shaped or irregularly wavy, usually fused laterally into rows and often stacked in tiers or arranged in rosettes.

Run a thumb over the top. It is distinctly hairy, felted or velvety, which is exactly what the species name records. Under a lens the tomentum appears as a dense mat of fine, matted, colourless to buff hairs. The surface is concentrically zoned in bands of grey, buff, tan and ochre, and older brackets frequently pick up a green cast from an algal film.

The margin is the freshest tissue and carries the strongest colour: bright yellow to orange when the fungus is actively growing, thin, wavy and often lobed. In dry or dormant material the margin fades to buff or pale grey and the whole bracket becomes hard and brittle.

Reading the Spore-Bearing Surface

Turn a bracket over, or bend it back if it is still attached, and look hard at the lower face. It should be completely smooth. Not poroid, not toothed, not gilled, not even wrinkled beyond a gentle undulation that follows the shape of the bracket. This smooth hymenium is the defining feature of the whole group and it is what makes crusts recognisable from twenty paces once you have the search image.

The colour is a warm yellow-ochre to buff-orange when fresh, becoming duller tan, buff or greyish as it dries and ages. Use a lens to confirm the absence of any pore mouths, since a very fine-pored polypore can look smooth to the naked eye.

The Scratch Test

This single action resolves most of the genus. Take a fresh, damp bracket and draw a knife tip or a fingernail firmly across the smooth underside, then wait half a minute.

In Hairy Curtain Crust nothing happens. There is no red juice, no blood-like droplet and no rusty red staining along the scratch. Several close relatives respond immediately by exuding a red to red-brown liquid, and that reaction is the fastest way to split the genus in the field. Note that the test only works on fresh, moist material, so rehydrate a dry bracket for a few minutes before drawing conclusions from a negative result.

Flesh, Texture and Section

Cut a bracket across with a sharp blade. The context is very thin, tough, leathery, and pale buff to ochre, homogeneous apart from the hairy layer on top. The whole structure is pliable when wet and hard and snappable when dry, and it revives on rewetting rather than rotting, which is why old brackets persist for many months. There is no distinctive smell.

Taking a Spore Print

Crusts do produce prints, though you have to work for them. Cut a fresh, actively growing bracket free with a little of the wood attached, lay it hymenium down on black card or a glass slide, cover it with a container to keep the humidity up, and leave it overnight. The deposit is white and often sparse, so a dark background is essential.

Under the microscope the spores are small, smooth, cylindrical to slightly sausage-shaped, roughly 5 to 8 by 2 to 3 micrometres, and amyloid, staining blue-grey in Melzer reagent. The hymenium contains no cystidia of the bristly, dark, thick-walled kind that characterise some superficially similar crusts.

Substrate, Season and Ecology

This is a saprotroph, and an occasional wound coloniser, of dead broadleaf wood. Oak is the classic host, followed by beech, birch, hazel, ash and sweet chestnut; conifer records are rare and should prompt a second look. Search fallen limbs, standing dead branches, log stacks, coppice stools, stumps and freshly cut ends. It is visible all year and fruits mainly from autumn through to spring.

Ecologically it is one of the earliest colonisers of newly dead broadleaf wood, causing a white rot that bleaches the timber and eventually leaves pale pockets of soft fibre. Split a colonised branch and you may see thin dark demarcation lines snaking through the wood where the mycelium meets a rival decayer.

It also hosts a parasite worth knowing. The gelatinous yellow-orange lobes of the yellow brain fungus Tremella aurantia erupt through Stereum colonies on oak, so a lump of yellow jelly on a branch is often a prompt to look for the crust underneath it.

Separating the Look-Alikes on Morphology

Stereum gausapatum, Stereum rugosum and Stereum sanguinolentum. All three release a red to red-brown juice when the fresh hymenium is scratched. Stereum gausapatum is largely resupinate with narrow reflexed edges on oak; Stereum rugosum is almost entirely flat, thicker and more brittle, on hazel and oak; Stereum sanguinolentum grows on conifer wood.

Stereum subtomentosum. Larger, more regularly fan-shaped brackets to 7 cm with a softer, more velvety, greyish top and a paler cream margin, typically on willow and alder in wet woodland. Rub its hymenium and it bruises yellow rather than staying inert.

Stereum ochraceoflavum. Small, thin, whitish-grey hairy brackets on slender dead twigs of oak and hazel, with a much paler, greyer hymenium.

Trametes versicolor and Trametes hirsuta. Superficially identical from above, with tiered zoned hairy brackets, but the underside is white and covered in fine round pores.

Chondrostereum purpureum. Also has a smooth underside, but it is lilac to purple when fresh and softer and more gelatinous in texture.

Hymenochaete rubiginosa. Dark rusty brown to almost black, rigid and brittle, on oak stumps, with a dark brown hymenium that is minutely velvety under a lens because of dark thick-walled setae.

Xylobolus frustulatus. Forms hard, pale, tile-like plates separated by cracks on the exposed heartwood of old oak, quite unlike a hairy bracket.

Phlebia radiata. Flat, waxy, orange to pinkish, with radiating wrinkles and ridges rather than a smooth surface.

Field Checklist

Dead broadleaf wood, any season. Effused-reflexed crust forming tiered wavy brackets 1 to 4 cm across. Upper surface hairy and concentrically zoned, with a bright yellow-orange growing margin. Lower surface completely smooth, yellow-ochre, without pores. No red exudate when scratched fresh. Thin leathery flesh that revives on wetting. White amyloid spore deposit with small sausage-shaped spores.