Milk-white Toothed Polypore Identification Guide

The Setting and the First Impression

This is a fungus you find by turning things over. Walk a hedgerow, a scrubby woodland edge or a storm-damaged plantation and start examining fallen branches, especially the underside of dead limbs that are still off the ground and the attached dead branches hanging in the crowns of broadleaved trees. The Milk-white Toothed Polypore is one of the commonest wood-rotting crust fungi of temperate hardwood, and once you have your eye in you will find it on almost every walk.

The first impression is of a long white or cream patch spreading along the wood, sometimes for ten or twenty centimetres, with a row of small shelves peeling away from the upper edge like a line of tiny hoods. The surface facing you is not smooth and not obviously pored; it looks rough, torn, and bristly, as though a pore layer had been dragged sideways. That torn, spiky appearance is the whole identification in miniature.

Reading the Overall Form

Start by classifying the growth habit, because this species straddles two categories. In many collections the fruit body is entirely resupinate: a flat crust lying tight against the wood, following every bump and crack, with a thin, fringed, white margin that fades into a fine cottony fuzz on the bark.

In other collections, especially on the undersides of branches, the upper edge lifts away from the substrate to form effused-reflexed brackets. These caps are small, projecting only 5 to 20 mm, semicircular or elongated, often fused laterally into wavy tiers that run along the branch. The upper surface of a reflexed cap is white to cream, finely hairy or velvety-tomentose, sometimes with faint concentric zoning, and it discolours to buff, dingy ochre or greyish with age or when algae colonise it.

A single fruit body may show both states along its length, so do not treat crust form and bracket form as different fungi.

Reading the Spore-bearing Surface

This is where the species is made. Look at the fertile surface with a hand lens.

In the youngest, thinnest parts near the growing margin the surface is genuinely poroid: small, angular, thin-walled pores, roughly two to four per millimetre. Very quickly, however, the pore walls split and break down. The dissection runs unevenly, so the walls tear into flattened, blade-like or spine-like projections that hang away from the surface. These are irpicoid teeth, and they are the classic feature: 1 to 3 mm long, flattened rather than cylindrical, often ragged or split at their tips, sometimes fused into short ridges or into partial maze-like alveoli near the margin.

Colour is white to cream when fresh, drying to buff, pale ochre or a faint yellowish tan. There is no pink, no orange, no violet and no grey. The teeth are firm, slightly brittle when dry, and they soften when wetted.

Run a fingertip lightly over the surface: it feels rasp-like. Then compare the margin, where pores may still be intact, with the older centre, where teeth dominate. Documenting that gradient in one specimen is far more convincing than a photograph of either state alone.

Flesh, Structure and Colour Change

Slice a bracket vertically. The flesh is very thin, usually less than 1 mm and rarely more than 2 mm, white, tough and leathery-flexible when fresh, and hard and rigid when dry. Between the tomentose upper surface and the tooth layer you may see a thin darker line under a lens in some material, but the tissue is essentially homogeneous white.

There is no latex and no bruising reaction. The fruit body does not blacken, redden or blue when cut or handled. What it does do is change with moisture: dried material becomes brittle and pale, then rehydrates and softens after rain, and old specimens weathering on wood take on a dirty cream or grey-buff cast that has more to do with age and algae than pigment.

Taking and Reading a Spore Print

Crust and bracket fungi can be printed, but it takes patience. Cut a piece of the colonised branch with a fresh, actively growing fertile surface, and suspend it teeth-downward a centimetre or two above a glass slide or a sheet of dark paper inside a closed box with a damp paper towel to hold humidity. Leave it overnight at cool room temperature.

The deposit is white and often sparse. Under the microscope the spores are small, smooth, hyaline, thin-walled, and cylindrical to narrowly ellipsoid, roughly 4 to 6 by 2 to 3 micrometres, with no reaction in iodine-based mountants. If you can also see the hyphal system, you will find thick-walled skeletal hyphae mixed with clamped generative hyphae, and characteristically encrusted cystidia projecting among the basidia, which are a reliable microscopic confirmation.

Substrate, Season and Ecology

The Milk-white Toothed Polypore is a white-rot decomposer of dead hardwood. It has an extremely broad host range across broadleaved trees, appearing on ash, beech, willow, poplar, elm, birch, hazel, apple, cherry, oak and many others, and turning up occasionally on conifers. It colonises small to medium branches most often, including attached dead branches in the canopy, and also fence posts, sawn timber and cut ends of stacked wood.

As a white-rot fungus it degrades lignin as well as cellulose, bleaching the wood to a pale, fibrous, spongy mass. It is often an early coloniser of branches that die while still attached, entering through pruning wounds and dead snags, and it can persist in the wood for years.

Fruit bodies form mainly from late summer through winter but are effectively perennial in their toughness: dried, weathered crusts remain identifiable on branches all year, and they revive to produce spores when rain returns. That year-round presence makes it one of the best species for winter fungus forays.

Separating It from the Look-alikes

Schizopora paradoxa is the closest match and the commonest confusion. It is strictly resupinate and almost never forms projecting caps with a hairy upper surface. Its fertile surface tears into irregular, maze-like, often blunt-toothed structures rather than into distinctly flattened, hanging blades, the texture is softer and more waxy-fibrous, and its spores are broader and shorter.

Steccherinum ochraceum has a similar effused-reflexed habit but its teeth are ochre, salmon or apricot-tinted rather than white, and the whole fruit body flushes warm orange-pink when fresh.

Trichaptum biforme grows on hardwood with a toothed to lacerate fertile surface, but fresh material is distinctly violet or lilac at the margin and on the teeth, and the caps are larger, more clearly zoned and hairier.

Bjerkandera adusta shares the thin effused-reflexed habit and white tomentose caps, but its fertile surface is grey to smoky black and remains truly poroid, and the flesh shows a dark line above the tubes.

Hyphodontia and other white toothed crusts are thinner, softer and never form projecting brackets, and they need microscopy to place confidently.

Climacodon and Hericium species have far larger fruit bodies with long, pendulous, cylindrical spines, not short flattened blades on a thin crust.

Quick Field Checklist

• On dead hardwood branches, often the underside or attached dead limbs
• Long white to cream crust, frequently with small tomentose shelves along the upper edge
• Fertile surface starts as angular pores and tears into flattened, ragged teeth 1 to 3 mm long
• Pure white to cream and buff, with no pink, orange, violet or grey tones
• Very thin, tough, leathery white flesh; white spore print with small cylindrical spores