Coral Tooth Fungus
Hericium coralloides
Also called comb tooth, coral hericium, coral spine fungus
A delicately branched white fungus whose thin arms carry short spines in neat rows along their undersides. It grows on dead broadleaf wood and looks like a piece of white marine coral fixed to a log.
Overview
The Coral Tooth Fungus is the most finely built of the common Hericium species. Where its relatives form heavy clumps or single shaggy cushions, this one produces an airy, repeatedly forking framework of slender branches, each hung with short spines. The overall impression is of white coral or an intricate lace, and mature specimens can spread 10-30 cm across a fallen trunk while remaining remarkably light in construction.
Hericium belongs to the Russulales, so despite its coral-like appearance it is more closely related to the brittle-gilled Russula mushrooms than to the true coral fungi in Ramaria and Clavulina. The connection is confirmed microscopically by its roughened, amyloid spores.
It is a good example of convergent form in fungi: branching maximises the surface area available for spore production on an exposed log, and the pendent spines let spores fall freely into moving air. The species is widespread across the temperate Northern Hemisphere and is a reliable autumn sight on large decaying hardwood logs.
How to identify it
Fruiting body
No cap is formed. From a small tough basal attachment on wood, the fungus branches repeatedly into thin, spreading, often slightly flattened arms that fan outward in a loose open network. Overall width is commonly 10-30 cm. Fresh material is white to ivory, ageing cream, then yellowish or pale tan, and browning at the tips as it dries.
Spines
Spines are short, mostly 0.3-1 cm, fine and soft, and they hang in tidy rows or combs along the lower sides of the branches rather than being bunched into terminal tufts. This even, comb-like distribution along the branch length is the single most useful field character for the species.
Flesh and spore print
The flesh is white, soft and slightly elastic in the branches, becoming tougher at the point of attachment. There is no marked colour change on cutting, though bruised or old parts discolour yellowish to brownish. The spore print is white; spores are small, subglobose, minutely ornamented and amyloid, staining blue-grey in iodine reagents.
Where and when it grows
Look for it on dead broadleaf wood: large fallen logs, standing dead trunks, stumps and occasionally wounds on living trees. Beech and maple are classic substrates, with oak, birch, ash, elm and poplar also used. It favours shaded, humid situations where big logs stay damp, so old-growth and long-unmanaged woodland produce it far more reliably than tidied plantations.
The fruiting season is late summer into autumn, sometimes persisting into early winter where frosts are late. The species is broadly distributed across Europe, temperate Asia and North America, though it is uncommon enough in intensively managed forests that it is used as an indicator of woodlands rich in large deadwood.
Ecological role
This is a saprotrophic white-rot fungus, occasionally behaving as a weak wound parasite. Its mycelium colonises the interior of fallen hardwood trunks and breaks down lignin as well as cellulose, bleaching the wood and leaving it soft, pale and spongy. Decay of this type is essential to nutrient cycling in broadleaf forest, releasing carbon and minerals locked in heavy timber and softening logs so that insects, mosses and seedlings can colonise them.
The visible coral-like structure is only the reproductive stage, appearing after the mycelium has occupied a substantial volume of wood, which is why fruiting is tied to big, long-dead logs rather than small branches. Because it depends on a continuous supply of large deadwood, populations decline sharply where fallen trunks are removed.
Similar species
Bear's Head Tooth (Hericium americanum) is the nearest relative in appearance but has thicker branches and much longer spines, 1-4 cm, gathered into dense tufts at the branch tips instead of running in rows along the branches. Lion's Mane (Hericium erinaceus) forms a single unbranched mass of long spines and cannot be confused once the branching plan is examined. Hericium abietis has the same general branched habit but is larger, creamier and fruits on conifer wood.
True coral fungi in Ramaria and Clavulina also branch but have smooth fertile surfaces on branches that taper to blunt or antler-like tips, with no hanging teeth, and Ramaria usually grows from soil with yellow, ochre or pinkish tones and a yellowish spore print. The white, spine-bearing undersides plus a wood substrate settle the identification.