Bear's Head Tooth

Bear's Head Tooth is a Hericium, a genus of white toothed fungi that abandon the usual cap-and-stalk plan entirely. Instead of a cap with gills, the fruiting body is a branched, coral-like structure anchored to wood by a tough basal knob, with the spore-producing surface spread over long soft spines that dangle from the branches. From a distance a mature specimen looks like a frozen white waterfall on the side of a trunk.

The genus belongs to the Russulales, an order better known for the brittle-fleshed Russula and Lactarius mushrooms. That relationship is invisible in the field but shows up in microscopic detail: Hericium spores are ornamented and amyloid, staining blue-black in iodine, exactly as in its brittle-gilled relatives.

Within the genus, Hericium americanum occupies the middle ground between the unbranched H. erinaceus and the finely branched H. coralloides. It is the classic large eastern North American species, and its combination of stout branching plus very long spines clustered at the branch ends is the feature to fix in mind.

Fruiting body

There is no cap. The whole structure is 10-40 cm across, occasionally larger, and hangs or bulges from a wound or cut end of wood. From a short, tough, whitish base the fungus divides repeatedly into thick arms, and these arms end in dense terminal tufts of spines. Fresh growth is pure white, ageing through cream to yellowish, tan and finally brownish as it dries or is frosted.

Spines

The spines are the key character. They are long, 1-4 cm and sometimes more, soft, slender, straight and pendent, and they are clustered mainly at the tips of the branches rather than being spread evenly along their lengths. Long, drooping, tuft-like clusters of this kind give the species its shaggy bear's-head appearance.

Flesh and spore print

The flesh is white and fairly firm, becoming tough and slightly stringy toward the anchoring base, and it does not change colour dramatically when cut, though the whole fungus discolours yellowish to ochre with age. The spore print is white; the spores are round to broadly ellipsoid, finely roughened and amyloid.

This fungus is a hardwood specialist. It appears on wounds and broken limb scars of living trees, on standing dead trunks, and on large fallen logs and stumps, with beech, maple, oak and other broadleaf trees among the most frequent hosts. It often fruits high on a trunk, so a fresh specimen may be spotted well above eye level, and the same wound can produce fruiting bodies for several seasons in a row.

The main season is late summer through autumn, extending into early winter in mild years, with fruiting triggered by cooling temperatures and sustained rain. It is a species of eastern North America, common in the deciduous and mixed forests from the Great Lakes and southern Canada south through the Appalachians.

Hericium americanum is a white-rot fungus that can act both as a wound parasite on living trees and as a saprotroph on dead wood. Its mycelium enters through storm damage, pruning wounds or broken branch stubs and works into the heartwood, degrading lignin along with cellulose and leaving the residual wood pale, soft and fibrous. Because heartwood is already non-living tissue, an infected tree can carry the fungus for many years while continuing to grow.

That slow internal decay is ecologically valuable: it hollows trunks and creates the cavities used by nesting birds, bats and denning mammals, and it recycles the most decay-resistant fraction of hardwood timber. The fungus fruits when the colonised wood is well established, which is why finds are usually associated with old trees, large logs and long-standing wounds rather than freshly fallen material.

The closest match is the Coral Tooth Fungus (Hericium coralloides), which builds a much more delicate, open, lacy framework of thin branches with short spines, under about 1 cm, arranged in rows along the undersides of the branches rather than bunched at the tips. Lion's Mane (Hericium erinaceus) is unmistakably different in plan: a single unbranched cushion or ball of very long spines hanging from one point of attachment, with no branching arms at all.

Hericium abietis has a similar heavy branched build and long spines but fruits on conifer wood, especially fir and hemlock in western North America, and often reaches a considerably greater size with a creamier tone. Branched white coral fungi such as Ramaria species can look superficially similar from a distance, but their branches taper to blunt or pointed tips and carry a smooth fertile surface, with no free-hanging spines anywhere.