Coral Tooth Fungus Identification Guide

The First Impression

You almost always see this one before you see anything else in the wood. Working along a fallen beech or maple trunk in early or mid autumn, you catch a patch of pure white on the shaded flank or underside of the log - not the flat crust of a resupinate fungus, but something with volume and depth, hanging out from the wood like a frozen splash or a lace shawl draped over the bark. From ten metres it reads as a bright white lattice; from two metres you can see that it is built of many slender branches, and that every branch is fringed underneath with rows of small hanging spines.

That is the whole identification in one look: a branched, coral-like, snow-white fungus with teeth instead of gills or pores, growing on dead hardwood. Nothing else in a temperate wood does exactly that, and the remaining work is simply confirming which member of the genus you have.

The Architecture of the Fruit Body

Rather than a cap and stem, this species builds a branch system. The whole structure is typically 10 to 30 centimetres across, occasionally reaching 40 on a well-rotted trunk, and it is usually wider than it is tall - it spreads laterally along the log rather than piling up.

Trace it back to the wood. Everything arises from a single tough basal mass, sometimes barely visible, which plugs into a crack, a broken branch stub or the cut end of a trunk. From that base a few main stems emerge and then fork repeatedly, the divisions becoming finer and more delicate outwards. The branches are somewhat flattened rather than round in section, slightly translucent when very fresh, and the overall effect is open and airy - you can see through the structure in places. Old specimens sag and mat together as they take up water.

Reading the Spines

Take a branch tip in your fingers and look at its underside with a hand lens. The spore-bearing surface is not gills, not pores and not a smooth skin, but a fringe of soft, downward-hanging teeth.

The critical detail is how the teeth are arranged and how long they are. On this species the spines are short - roughly 3 to 10 millimetres, occasionally to 15 on a vigorous specimen - and they are set in tidy rows all along the undersides and lower sides of the branches, from near the base right out to the tips. They are not gathered into dense terminal tufts, and they do not hang in long curtains. Run a finger along a branch and you should feel a comb of small even points for the whole length of it.

Individual teeth are needle-like and taper to a fine point; they are soft and slightly rubbery when fresh, hardening as the fruit body dries.

Colour, Texture and Ageing

Fresh material is pure white to cream, occasionally with the faintest pinkish or grey cast where the branches are thickest. There is no bruising reaction of the sort you would look for in a bolete or a milkcap - no blue, no red, no instant blackening. What happens instead is a slow, cumulative discolouration with age and handling: the tips of the teeth go cream, then pale yellow, then buff and finally ochre-brown, and the branch surfaces follow. A specimen that is dull tan all over and beginning to sag is simply an old one, not a different species.

Cut through a main branch. The flesh is white throughout, fibrous and tough at the basal attachment - almost corky where it enters the wood - and softer, more spongy and full of water in the branches. It does not change colour on the cut face. Odour is faint and pleasantly fungal.

There is no stipe in the ordinary sense, no ring, no veil, no volva and no annular zone; if you are looking for those, you are asking the wrong questions of this fungus.

Taking a Spore Print

Because the spore-bearing surface faces downwards on hanging teeth, printing is straightforward but needs the right background. Cut a branch section carrying plenty of spines, rest it teeth-downwards over a piece of black card or dark glass with a couple of matchsticks under it to keep the teeth clear of the surface, cover the lot with a bowl to keep the air still and humid, and leave it several hours or overnight.

The deposit is white, so it is nearly invisible on paper and obvious on black. Under a microscope the spores are small, subglobose to broadly ellipsoid, minutely roughened, and stain blue-grey in iodine reagent - an amyloid reaction that is standard for the genus.

Substrate, Ecology and Season

This is a white-rot decomposer of dead hardwood. It attacks the lignin as well as the cellulose, leaving the residual wood pale, soft and stringy. Look for it on fallen trunks and large limbs of beech, maple, birch, ash, lime, elm and sometimes oak, and also on wounds, broken branch stubs and dead patches on standing trees where the heartwood is exposed.

It prefers substantial timber over small branches, and shaded, humid, undisturbed situations - which is why the best places for it are old woodland with plenty of large fallen wood left in place, ravines, and damp north-facing slopes. Once it has colonised a trunk it commonly fruits from the same wound or crack for several years running, so it is worth marking a productive log and coming back.

The main season is late summer to late autumn, peaking after the first cool damp spells of September and October. Where autumn frosts arrive late, individual fruit bodies can persist, discolouring, well into early winter.

Separating It From the Rest of the Genus

Within Hericium, work on two features: is the fruit body branched or not, and how long are the spines relative to the branches.

Hericium erinaceus is unbranched. It forms a single rounded cushion or head attached to a wound on a standing trunk, usually of beech or oak, and the spines are long - one to five centimetres - and all hang together from the face of that one mass, giving a shaggy pom-pom outline. If your fungus has a branch system, it is not this.

Hericium americanum is branched like the Coral Tooth Fungus, but its spines are much longer - commonly one to four centimetres - and, decisively, they hang in dense clusters at and near the branch tips rather than in even rows along the whole length of the underside. The result is a chunkier, more tasselled silhouette. It is a north-eastern North American species.

Hericium abietis and its relatives are branched with long spines but grow on conifer wood - fir, spruce and hemlock - which alone separates them in most regions, and they are often larger and more cream-tinted.

Look-alikes Outside the Genus

Artomyces pyxidatus, the crown coral, is white to pale ochre, branched, and grows on dead hardwood, so it fools people at a distance. Look at the surface: it is smooth, with no teeth at all, and each branch ends in a small crown or coronet of upward-pointing prongs. The Coral Tooth Fungus never makes those crowns, and always has spines.

Ramaria species are also branched and coral-like, but they grow from soil rather than from wood, their branches are smooth-surfaced, and most are coloured ochre, yellow, tan or violet rather than white.

Climacodon septentrionalis does have teeth, but it builds them under thick shelving brackets stacked in tiers on the trunk of a living tree - a bracket fungus with a toothed underside, not a coral.

Mucronella species produce clusters of small white spines hanging directly from the surface of dead wood with no branching structure whatsoever, and Pseudohydnum gelatinosum is a gelatinous grey-brown tongue with tiny blunt teeth beneath.

The Short Version

White, branching, growing from dead hardwood, spines 3 to 10 millimetres set in rows along the undersides of the branches all the way from base to tip, white flesh that yellows slowly with age, white spore deposit, autumn. Confirm branching, then measure a spine, and the genus falls into place.