White Cheese Polypore Identification Guide

The Setting and the First Glance

Mid to late summer in damp broadleaved woodland, walking along a mossy fallen birch trunk. What catches the eye is a small, startlingly white shelf on the upper side or the flank of the log, bright against wet bark. Fallen and standing dead birch is the classic substrate, with beech, alder, hazel, maple and other hardwoods also producing it.

The first impression is soft rather than woody. Where most brackets read as hard and permanent, this one looks like a lump of set fat, fresh plaster or a slab of soft cheese pressed onto the log. Pinch it and it squashes, springs back partly, and leaves your fingers wet.

Reading the Cap

Brackets are 2-10 cm across and 1-4 cm thick at the attachment. The outline is semicircular, kidney-shaped or fan-shaped, and they are sessile, meaning broadly attached to the wood with no stipe at all. Single brackets are common, and short overlapping rows occur on a favourable log.

The upper surface is white to cream, finely velvety or minutely felted when young, and it smooths out with age, sometimes becoming faintly wrinkled or lumpy. It is either unzoned or shows only the faintest concentric shading, never the strong banded zoning of a Trametes. The margin is thick, blunt and even rather than thin and sharp.

Age changes it noticeably. Old specimens turn pale straw or dingy yellowish-buff, shrink as they lose water, and finish as light, hard, distorted lumps still attached to the log.

Reading the Pore Surface

Turn the log or crouch beneath the bracket. The underside is a pore surface, white to cream and sometimes greying very slightly with age. The pores are small and round, about 3-5 per millimetre, which means you need a hand lens to resolve them properly; to the naked eye the surface looks almost smooth and matt. Near the point of attachment they can become angular or slightly elongated.

Tubes are shallow, roughly 2-6 mm deep, and they do not separate cleanly from the flesh as a distinct sheet.

Press the pore surface firmly with a thumb and watch. Nothing much should happen. It stays white, or at most goes very faintly buff. Any blue-grey, pink, red-brown or blackening reaction moves you out of this species immediately, so this negative result is genuinely informative.

Flesh and the Cheese Character

Slice the bracket vertically from the upper surface down through the tubes. The flesh is homogeneous white, with no distinct upper crust and no dark line separating the cap surface from the flesh beneath. Fresh material is soft, watery and juicy: squeeze a piece over your palm and drops come out.

Now the character behind the common name. As the fruit body dries, that soft wet flesh becomes light, chalky, brittle and remarkably like a piece of dry cheese in texture, breaking with a crumbly snap. An old dried bracket is startlingly light in the hand for its bulk. That transition from waterlogged and squashy to chalky and weightless is a useful confirmation on a specimen you have brought home.

Odour is faintly and pleasantly fungal, with no chemical or sharp note.

Taking and Reading a Spore Print

Choose a fresh, actively growing bracket; old dried material will give you nothing. Cut it free with a piece of the wood if necessary, prop it pore-side down over a strip of dark paper or a glass slide, and shut it in a covered box overnight so the humidity stays high.

The print is white and often sparse. Under the microscope the spores are small, allantoid, meaning curved like a tiny sausage, smooth, colourless and around 4-5 by 1.5 micrometres, and they do not turn blue in iodine. The hyphal system is monomitic with clamp connections, which is consistent with the soft, easily squashed texture: there are no binding or skeletal hyphae to make it tough.

Substrate and Season

This is an annual saprotroph causing a white rot in dead hardwood. It does not build up perennial layers, so you will never see the stacked strata of tube layers that a Fomes or Ganoderma accumulates: one season, one tube layer, then decay. Fruiting runs from midsummer to late autumn, and blackened, shrivelled remains persist on logs into winter.

Look on fallen trunks and branches, on standing dead stems, and on cut stacked wood in damp woodland. Birch is the tree to check first in northern temperate woods.

Separating It from Look-alikes on Morphology Alone

The Postia caesia group, the blue cheese polypores, is the nearest confusion in build. They are white brackets of similar softness, but they carry grey-blue tints somewhere on the cap or pore surface and they bruise blue-grey where handled, and they occur mainly on conifer wood.

Postia fragilis is likewise a soft white bracket, but it stains reddish-brown to nearly black where touched, and it too favours conifers.

Postia tephroleuca is greyish-white overall, a little tougher and drier, without the juicy fresh texture.

Trametes species, including T. gibbosa and T. pubescens, are the commonest general mix-up. They are thin, tough and leathery; you can bend them and they flex rather than squash, they are dry rather than watery, and most show concentric zoning. Trametes pubescens is cream and velvety and comes closest, but the texture test settles it in one pinch.

Bjerkandera adusta has a grey pore surface that darkens to almost black when bruised, and a thin dark line visible in section between cap surface and flesh.

Polyporus and Cerioporus species carry a definite stipe, central or lateral, rather than being broadly sessile.

Irpex lacteus and Steccherinum species start with pores but break down into ragged teeth and spines as they mature, and they tend to spread in resupinate sheets rather than forming neat thick shelves.

A Practical Field Sequence

Confirm dead hardwood, ideally birch, in summer or autumn. Confirm a soft, sessile, white, unzoned, blunt-margined bracket that squashes when pinched. Lens the underside for small round white pores at 3-5 per millimetre. Press hard and confirm no blue, red or black bruising. Section it and confirm homogeneous white flesh with no dark line. Print overnight and confirm white.