Rosy Crust Identification Guide

The Setting and the First Glance

Rosy Crust is a fungus you find by handling wood rather than by scanning the ground. The typical encounter is a damp winter or early spring walk through scrubby broadleaf woodland or a hedgerow, where you pull down a dead but still attached branch of hazel, gorse, ash or blackthorn, turn it over, and find a patch of bright coral-salmon paint spread along the bark. Nothing else in the same microhabitat is quite that colour.

Because it lives on small-diameter dead wood that is still in the air, hedges, scrub edges, gorse stands, coppice regrowth and the lower dead branches of young trees are all productive. It also turns up on recently fallen brash on the woodland floor, and on bramble canes and elder. Its abundance and its long fruiting season make it one of the first corticioid crusts most people learn.

Growth Form

Start by describing the shape, because for crust fungi the growth form is half the identification. Rosy Crust is resupinate and effused: it lies completely flat against the bark with no cap, no stalk and no free edge, spreading as irregular patches from a few millimetres to well over ten centimetres long. Neighbouring patches merge into long strips running with the grain of the branch.

It is thin, generally only 0.1 to 0.5 mm thick, and firmly stuck down. When fresh and wet it is soft and slightly waxy, almost gelatinous under a fingernail. As it dries it hardens, contracts and often cracks into small polygonal plates, and the colour shifts toward duller ochre or brick. The margin is usually a little paler than the middle, whitish-pink, and may be finely fibrillose or sharply defined depending on how fast the patch is growing.

Colour and the Rehydration Test

Colour is the headline character: bright salmon, coral, orange-pink or a soft flesh-pink when the fungus is fresh and damp. Dried patches lose most of the pink and can look like a dull orange-brown stain, which is where people give up too early. Put a drop or two of water on a dried patch and wait a minute. Rosy Crust rehydrates readily and the pink floods back, and the surface softens again. That simple test rescues a great many winter collections.

Reading the Spore-bearing Surface

There is no gill, pore or tooth layer to interpret here, because the entire exposed face of the crust is the hymenium. What you are looking for with a lens is texture. Rosy Crust is smooth to very slightly bumpy or low-tuberculate, without radiating wrinkles, veins or ridges. Under magnification the surface looks minutely granular and matt rather than glossy, an effect produced by microscopic sterile elements projecting through the surface.

Absence of structure is diagnostic in its own right. If you see radiating folds and veins, a raised gelatinous body, tiny teeth, or discrete cushion-shaped lumps rather than a continuous sheet, you are somewhere other than Peniophora incarnata.

Spore Print and Microscopy

Getting a print from a crust takes patience but is possible. Choose an actively growing, fresh patch, break off a short section of twig, and suspend it hymenium-down over a glass slide or dark card inside a closed container with a scrap of damp tissue to keep the humidity up. Leave it overnight in a cool place. The deposit is white to very pale ivory.

The microscope makes the identification airtight. Spores are cylindrical and curved, roughly 8 to 12 by 3 to 4 micrometres, smooth, colourless and thin-walled. More distinctive still are the sterile elements: thick-walled cystidia heavily encrusted with crystals that project well beyond the hymenium, together with branched, coral-like sterile hyphae and smooth, oily gloeocystidia. Clamp connections are present. Crystal-capped cystidia in a bright pink crust on hardwood twigs is a very short list of candidates.

Substrate, Season and Ecology

The substrate is dead attached or very recently fallen branches of broadleaved trees and shrubs, with hazel, ash, gorse, oak, willow, elder, blackthorn and bramble among the commonest. It is an early coloniser: it moves into small branches soon after they die, often while the bark is still intact, and it decays them as a white rot, leaving the wood pale, soft and fibrous rather than crumbly and brown.

Fruiting is essentially year-round in mild climates, with the best condition from autumn through early spring when humidity is high. On a single dead hazel branch it commonly shares space with other early colonisers, so expect to see it next to smooth grey crusts, black flask-fungus stromata and small disc fungi.

Separating the Look-alikes

Peniophora quercina grows on oak and is grey-lilac to dull purplish-flesh when moist, never coral. Its most useful habit is that the patch edges lift and curl away from the bark as they dry, exposing a dark brown to blackish under-surface. Rosy Crust stays flat and adherent.

Peniophora rufa occurs on aspen and poplar and forms discrete blister-like reddish cushions with raised, rounded outlines rather than a continuous spreading sheet.

Peniophora limitata is a species of ash, greyish to violet-brown, and characteristically has a sharply black-edged margin, so the patch looks as though it has been outlined in ink.

Cytidia salicina is a willow specialist. It begins as separate rounded discs that later coalesce, and it is a much darker blood-red to maroon, with a distinctly gelatinous, rubbery consistency.

Phlebia radiata overlaps in colour, sometimes appearing orange-pink, but it is thicker, rubbery-gelatinous, and strongly radially wrinkled with raised veins and a paler fringed margin. Its texture in the hand is completely different from a thin waxy film.

Corticium roseum on willow is a softer, thicker, matt rose-pink crust with a woolly margin rather than a waxy, adherent, coral-toned film.

One last trap: orange films of Trentepohlia algae on bark can be mistaken for a pink crust at a distance. Scrape a little with a knife tip. The alga is a powdery, dusty film that comes away as loose grains, while Rosy Crust peels or flakes as a coherent membrane.

Field Checklist

1. Dead attached broadleaf twig or small branch.
2. Flat, thin, adherent patch with no cap or edge lifting.
3. Coral to salmon pink when moist, restored by wetting when dry.
4. Surface smooth or slightly bumpy, never veined or toothed.
5. Waxy when fresh, cracking into plates when dry.
6. Under the microscope, curved spores plus crystal-encrusted cystidia.