Northern Tooth Identification Guide

First Impressions and the Setting

Northern Tooth is normally spotted from a distance and from the wrong angle. You are walking through mature hardwood forest, often on rich ground with plenty of sugar maple, and part-way up a living trunk there is a pale, shelving mass clamped to the bark, usually at an old wound, a pruning scar or a broken branch stub. Two to six metres is a typical height, which is itself informative: this is a species of standing living trees, not of logs on the ground.

From below it looks like a generic white polypore. The identification turns entirely on getting a look at the underside. Tilt your head, hold a phone camera up at arm's length, or find a fallen shelf beneath the tree, and the flat white surface you expected is instead a dense, downward-hanging pelt of soft spines.

Reading the Fruit Body

The fruit bodies are sessile: there is no stem at all, and the whole cluster grows out of a common swollen base wedged into the wound. Individual caps are 5-15 cm wide and occasionally 20 cm, 1-3 cm thick where they attach, semicircular to fan-shaped, and stacked in tight overlapping tiers. A vigorous cluster forms a rosette 30-40 cm across and can weigh several kilograms.

The upper surface is white to cream when actively growing and dries through pale buff to tan and eventually a dingy yellow-brown. Run a finger over it: it is roughened, matted-hairy or finely tomentose rather than smooth or varnished, and it is often radially furrowed and lumpy where neighbouring caps have fused. The margin is thick, blunt and inrolled while young, usually the palest part of the whole cluster.

The Spore-Bearing Surface

This is the diagnostic feature and it deserves a lens. Beneath each shelf hang crowded, soft, tapering spines 0.5-2 cm long, roughly three to five per millimetre at their bases, white to cream when fresh and drying yellowish-tan and brittle. On the lowest shelves the spines often run down onto the bark of the trunk itself.

Check that they are true spines rather than broken-up pores. Genuine teeth are free and independent from the base, taper to a point, and can be teased apart with a pin. Weathered specimens lose their spine tips and can look raggedly pored, so always examine fresh growth at the margin where possible.

Flesh, Base and Colour Change

Cut a shelf through vertically. The flesh is 1-2 cm thick, white, tough and fibrous, and in section is often faintly zoned into a softer upper layer and a denser lower one. Fresh material is moist and rubbery; dried material is corky and unpleasantly hard to cut. Squeeze a piece and it is spongy-fibrous rather than brittle.

There is no dramatic bruising reaction. Cut surfaces stay white or drift slowly to cream and buff over hours. The smell of fresh clusters is strong and pungent, becoming sharper and more sour as the cluster ages.

At the end of the season the whole mass shrivels, blackens and stays attached to the trunk over winter as a dark, hard shelf. Those blackened remains are a genuinely useful winter search image: find them and you know where to return in late summer.

Taking and Reading a Spore Print

Printing a bracket needs a slightly different technique from printing an agaric. Cut a small wedge with intact spines, prop or suspend it spines-downward over a sheet of black card in a closed box with a scrap of damp tissue, and leave it overnight. Black card matters because the deposit is white and sparse.

The spore print is white. Under a microscope the spores are very small, roughly 4-5 by 2-3 micrometres, smooth, ellipsoid and colourless, which is consistent across the toothed polypore relatives and mostly serves to confirm the group rather than the species. The macroscopic characters do the real work here.

Substrate, Season and Ecology

Northern Tooth is a heart-rot fungus of living hardwoods, overwhelmingly sugar maple, with beech and other maples as secondary hosts. It enters through wounds and dead branch stubs and decays the heartwood, producing a white, flaky, pocketed rot in the trunk while the tree continues to leaf out normally. A fruiting cluster is therefore evidence of extensive internal decay that has been running for many years.

Fruit bodies are annual, appearing from late summer into autumn, typically August to October, and reappearing in the same place on the same tree for years or decades. The habit of fruiting on a living standing trunk, well above the ground, is one of the strongest identification pointers you have before you even look at the spines.

Separating It From Look-Alikes

Spongipellis pachyodon (also placed in Irpex or Sarcodontia) is the sharpest trap: white, on living hardwood, sometimes shelving. Its underside, however, begins as flattened, angular, torn pores that split with age into irregular, flattened, plate-like teeth. They are broad and ragged rather than round and tapering, and the brackets are thinner and often mostly resupinate, spreading across the bark.

Hericium species are pure white masses of spines but have no cap at all. They hang as branched or cushion-like clumps with spines on all sides, with no tomentose upper surface and no shelving tiers.

Bondarzewia berkeleyi forms a huge shelving rosette, but it grows at the base of oaks rather than high on maple trunks, and its underside is pored.

Climacocystis borealis is a whitish shelving bracket of conifers with a pored underside and much softer, more watery flesh.

Laetiporus species are bright orange and yellow with pores.

Steccherinum ochraceum is toothed but tiny: a thin, ochre-pink, effused-reflexed crust on dead branches, with spines only 1-3 mm long.

The workflow is simple. Confirm the tree is a living hardwood and the fruiting point is up the trunk; confirm the shelves are tiered and broadly attached with a hairy upper surface; then confirm that the underside carries long, soft, free-hanging spines rather than pores or flattened plates.

Field Checklist

Tiered white to buff shelving brackets high on a living maple; roughened hairy upper surface; crowded soft white spines up to 2 cm long underneath; tough fibrous white flesh; strong pungent smell; white spore print; annual, late summer to autumn, blackening and persisting through winter.