Northern Tooth

Northern Tooth (Climacodon septentrionalis) is one of the most imposing wood fungi of northern temperate forests. It produces annual clusters of thick, fleshy brackets that are fused at a common base and stacked in tiers, so a single fruiting can stand half a metre tall and weigh several kilograms. From a distance it reads as an ordinary shelf fungus, but a look underneath reveals that the fertile surface is made of thousands of soft, downward-hanging spines rather than tubes or gills.

The genus Climacodon sits in the Meruliaceae, a family better known for thin resupinate crusts and wrinkled parchment-like fungi. C. septentrionalis is the outsized exception, and its combination of bracket architecture with a toothed hymenium makes it easy to place once seen. The specific epithet septentrionalis simply means "northern", reflecting its distribution across the cooler hardwood forests of the northern hemisphere.

Because it fruits from wounds and broken limbs well above head height, Northern Tooth is often spotted as a pale mass glowing against dark bark rather than found at ground level. Old fruitings dry in place, turning hard, ochre and cheese-like, and can persist on the tree well into winter as a bleached, shrunken remnant.

Fruiting body

Brackets are 10–30 cm across and 1–3 cm thick, semicircular to fan-shaped, and grow in dense overlapping tiers from a single fused attachment point. Whole clusters commonly reach 20–40 cm high. The upper surface is dry, matt and finely hairy to coarsely bristly, often with faint concentric ridging; colour runs from white and cream when fresh to dingy ochre, buff or tan with age.

Teeth

The underside carries crowded, soft, tapering spines 5–20 mm long, hanging vertically regardless of how the bracket is tilted. They are white to cream at first, ageing yellowish then dull brown, and become brittle as the fruiting body dries. The spines are the single most reliable field character separating this from any true bracket fungus.

Stipe & flesh

There is no true stalk; brackets narrow to a tough fused base attached directly to the wood. The flesh is white, fibrous and rather tough when fresh, drying corky to almost hard, and is often faintly zoned in section. Fresh specimens are notably moist and heavy.

Spore print

The spore print is white. Spores are small, smooth, ellipsoid to nearly cylindrical and thin-walled, released in quantity so that lower tiers are often dusted pale by those above.

Northern Tooth is a fungus of living, mature broadleaf trees rather than fallen wood. Sugar maple (Acer saccharum) is the classic host, with other maples, beech, birch, elm and occasionally walnut also colonised. Fruiting occurs from old pruning scars, frost cracks, broken branch stubs and other trunk wounds, frequently several metres above the ground.

It is most abundant in eastern and midwestern North America, where it is a familiar feature of old sugar bushes and street maples, and is also recorded across parts of northern Europe and temperate Asia. Fruiting runs from late summer into autumn, and the dried, blackening remains often stay attached to the trunk through winter.

This species is a parasite of living heartwood, causing a white rot that hollows the central column of the trunk while the sapwood and crown remain alive. Mycelium enters through exposed wood at wound sites, then spreads vertically through the heartwood, breaking down lignin and cellulose and leaving a soft, pale, stringy residue. Trees can carry the infection for decades before any external fruiting appears, so a single bracket cluster usually signals extensive internal decay.

Ecologically it is an important agent of hollow formation in old hardwoods. The cavities it creates become nesting and roosting sites for owls, woodpeckers, squirrels and bats, and the decay column returns locked-up carbon and minerals to the forest cycle. After the host finally dies, the fungus can persist saprotrophically in the standing snag for several more seasons.

The tiered bracket habit distinguishes it from the Hericium tooth fungi (Hericium erinaceus, H. coralloides), which produce cushions or branched coral-like masses of spines with no shelf-like caps at all. Spongipellis pachyodon also grows on hardwood and has a ragged, tooth-like fertile surface, but it is largely flattened against the wood with only small projecting caps, and its teeth are broader and more irregularly torn.

Laetiporus sulphureus shares the tiered shelf form and sometimes the same maples, but is bright orange and yellow with a smooth pored underside. Ganoderma applanatum forms hard, woody, grey-brown perennial brackets with fine white pores that bruise brown, and yields a brown spore print rather than white. Within the genus, Climacodon pulcherrimus is smaller, warmer buff-orange, and is a warm-temperate species with shorter teeth.