Netted Crust Identification Guide

The First Impression

Netted crust is the fungus you find when you turn over a dead hazel branch in a damp hedge and discover that its underside has been painted. The paint is soft, cream to white, and it covers a stretch of the branch like a thin skin. Run a fingernail under the edge and the whole sheet lifts away in one piece, still holding its shape. That peelability, more than any single measurement, is what people remember about Byssomerulius corium.

The setting is broadleaf woodland, hedgerow, scrub and river-edge thicket in the temperate Northern Hemisphere. It is a common, year-round fungus and one of the first crusts most people learn, because it appears reliably on the same fallen twigs and branches season after season.

Growth Form

Start with the overall shape, because this is a corticioid fungus and there is no cap-and-stem architecture to work through.

The fungus grows resupinate, that is, flat against the wood with the spore-bearing surface facing outward. Patches begin as small cream spots a centimetre or two across and expand and merge until they sheath an entire branch section, sometimes 20 cm or more.

Very often the upper edge of a patch lifts free of the wood to form a narrow bracket, so the fungus becomes effused-reflexed. These reflexed caps are small, typically 2 to 10 mm deep, thin, wavy, and can run in overlapping tiers along a horizontal branch. Their upper surface is white to greyish, finely hairy or felted, sometimes faintly zoned, and older ones frequently turn green from a coating of algae.

The Spore-Bearing Surface

This is where the common name comes from, and it is worth studying with a lens.

When young and fresh the hymenial surface is nearly smooth, waxy and cream, sometimes with a delicate pinkish, buff or pale lilac tinge. As it matures it develops low, blunt, rounded folds. Those folds branch and rejoin, meeting each other at angles and enclosing shallow irregular pits, so the surface becomes a low net of ridges. This pattern is called merulioid, and it is the classic condition here: not true pores with defined walls, and not spines or teeth, but an anastomosing mesh of soft wrinkles.

Colour of the mature hymenium is cream, buff, ochre-cream, ageing to dull ochre or pale tan, and drying darker and harder.

The Margin

Check the edge of the patch. In fresh material it is white, sterile, and distinctly fibrillose to byssoid, meaning it looks cottony or downy, breaking up into fine radiating threads that fade out onto the bare wood. That soft cottony fringe is a good confirming feature and is part of why the genus is named Byssomerulius.

Texture, Attachment and Flesh

Press the surface. Fresh material is soft, waxy-membranous to slightly leathery, and yields a little. Dry material is stiff, hard and often cracked into a mosaic, and it rehydrates when wetted.

Now do the peel test. Slide a knife tip or fingernail beneath the margin and lift. Byssomerulius corium separates from the wood easily and comes away as a coherent sheet, sometimes several centimetres at a time. Most crust fungi cannot be removed without shredding.

The flesh itself is very thin, generally 0.1 to 0.5 mm, whitish, and shows no colour change when cut or bruised. There is no latex, no red bleeding, no blackening.

Taking a Spore Print

You cannot lay a crust gills-down, so adapt the method. Cut a short section of branch bearing fresh, pale, actively growing fungus. Suspend it hymenium-downward a centimetre or two above a piece of black card, using two blocks or the rim of a box, then cover the whole arrangement to keep it still and humid and leave it overnight.

The deposit is white and usually sparse; look at it in raking light. Under the microscope the spores are smooth, thin-walled, hyaline, cylindrical and slightly curved, that is, allantoid or sausage-shaped, about 5 to 7 by 2.5 to 3 micrometres, and they do not react in Melzer reagent. The basidia are club-shaped with four sterigmata and there are no cystidia of note.

Substrate and Season

The substrate range is broad but consistently broadleaf and consistently small-diameter. Hazel is the classic host; ash, willow, birch, oak, elder, blackthorn, bramble stems and many other shrubs and trees all serve. Look at fallen branches lying on damp litter and at dead attached branches still in the shrub layer, particularly on the shaded underside.

It fruits all year and is most conspicuous from autumn through spring when humidity is high and competing fungi are less abundant. It is a decomposer, part of the early to middle sequence that breaks down twigs and small branches on the woodland floor.

Separating the Look-Alikes on Morphology

Phlebia radiata. Often on the same fallen wood. It is brightly coloured in orange, salmon, pinkish or violet tones, waxy to gelatinous, and radially wrinkled outward from a centre rather than netted. It is firmly attached and will not peel cleanly.

Phlebia tremellosa. The closest visual match, since it too is merulioid with a white hairy reflexed edge. Separate it on texture and colour: it is markedly gelatinous, soft and translucent, and its hymenium is pinkish orange to salmon rather than cream-buff. It also favours larger stumps and logs over slim branches.

Stereum species. S. hirsutum and S. rugosum form leathery crusts and brackets on the same wood, but their spore-bearing surface is smooth, never a net of folds. They are tough, firmly attached, and S. rugosum releases red juice when the fresh surface is scratched.

Chondrostereum purpureum. Effused-reflexed like netted crust, but the hymenium is a distinctive purple to lilac-brown and smooth to slightly bumpy.

Cylindrobasidium laeve. Whitish-cream, also detaches quite readily, but the surface stays smooth to finely warted or tuberculate and never develops the branching ridge network.

Schizopora paradoxa and Xylodon species. Whitish-cream crusts on the same substrate, but their surface breaks up into irregular pores, split tubes or fine spines, and they are tightly attached to the wood.

Peniophora species. Smooth, waxy, often greyish pink to lilac, firmly attached, and typically cracking into small islands as they dry.

The working formula is therefore: cream to buff resupinate sheet on a broadleaf branch, low branching ridges enclosing shallow pits, white cottony margin, often a narrow hairy reflexed bracket edge, peels off the wood in one piece, and a white print of small curved spores.