Winter Polypore Identification Guide

First impressions and the setting

Winter Polypore is a small, unglamorous, cold-weather fungus of dead broadleaved wood, and you generally meet it when nothing else is fruiting. You are walking a bare winter wood, a hedgerow, a coppice or a scrubby riverside thicket, and on a fallen branch of hazel, birch, willow, beech or ash you see a small brown mushroom that at a distance looks like an ordinary agaric.

It is only when you tip it over that the fungus declares itself: instead of gills there is a fine, pale, spongy pore surface running a short way down the stem. That is the moment of recognition - a stalked, centrally stemmed polypore, no bigger than a small ordinary mushroom, on dead deciduous wood in winter.

A second impression that helps is texture. The whole fruit body is tough and leathery rather than fleshy. You cannot squash it; it flexes and springs back, and pulling it off the branch takes real effort.

Reading the cap

Caps are two to eight centimetres across, occasionally a little larger. They begin convex with an inrolled edge and flatten out, usually becoming shallowly depressed over the point of stem attachment, so that a mature cap is dished or funnel-like in the centre.

The colour is undemonstrative: greyish-brown, umber, dull tan, mouse-brown or blackish-brown, generally darker when fresh and wet and fading to buff or greyish as the fruit body dries. Old weathered specimens bleach considerably and can be almost grey.

The surface is dry and finely velvety or minutely downy when young, becoming smooth and sometimes finely wrinkled or radially streaked with age. There is no viscidity and no shiny lacquer.

The margin is worth examining with a lens on young material. It is often finely fringed, ciliate or minutely hairy, carrying a delicate row of short stiff hairs that wears off as the cap expands. In older caps the margin is thin, sometimes slightly incurved, occasionally splitting radially.

The pore surface

Turn the fruit body over. The hymenophore is tubular, not lamellate: a layer of shallow tubes opening as pores across the underside.

Colour is whitish, cream or pale grey when fresh, dulling to buff or pale brownish with age and drying. Bruised areas may darken slightly to dingy brown but there is no bright reaction.

The pores are small: usually two to four per millimetre, so with the naked eye the surface reads as a fine even sponge and you need a lens to resolve individual openings. They are angular to slightly elongated, and near the stem they often stretch and become radially arranged.

Attachment matters. The pore layer runs decurrent onto the top of the stipe for a few millimetres, tapering out rather than stopping abruptly. The tube layer itself is shallow, typically only one to two millimetres deep, and it separates poorly from the cap flesh because the two are continuous.

Stipe, base and flesh

The stipe is central, or occasionally slightly off-centre, one to four centimetres long and two to six millimetres thick, more or less equal and often slightly curved to bring the cap horizontal.

Colour is greyish-brown to pale brown, usually similar to or slightly darker than the cap, and the surface is finely velvety or minutely scurfy when young, particularly towards the base, becoming smoother with age. Critically, the base is not sharply black: it may darken to a dull brown, but it does not show the abrupt black boot found in some relatives, and that is one of the most useful separating characters in the group.

There is no ring and no volva. The stipe is solid, tough and fibrous throughout, and attaches directly to the wood, often at a small point where the mycelium has darkened the surrounding bark.

The flesh is thin, white to pale cream, tough, leathery and elastic. Cut it and nothing happens: there is no colour change, no latex, no reddening. When the fungus dries it becomes hard and horny, and old fruit bodies can persist on a branch in shrivelled form for weeks.

Taking and reading a spore print

Polypores print, but they demand patience and fresh material. Cut the stipe short, lay the cap pore-side-down on white paper, cover it with a bowl to hold humidity, and leave it overnight or up to twenty-four hours. Fresh actively growing fruit bodies deposit well; dried-out overwintered ones often deposit nothing, and a blank result is not evidence against the identification.

The print is white. Under a microscope the spores are cylindrical to narrowly ellipsoid and smooth, and the hyphal system is dimitic, with skeletal hyphae giving the fruit body its characteristic toughness.

Substrate and season

This is a saprotroph of dead broadleaved wood, causing a white rot. It favours fallen branches, small logs, and attached dead branches still in the canopy, most often of hazel, birch, willow, beech, ash, alder and other broadleaves. It has a marked preference for smallish diameter wood - the fallen twiggy material that accumulates in hedge bottoms and coppice - rather than massive trunks. Occasionally it is found on conifer wood.

The season is the point of the name. It fruits in the cool part of the year, appearing from late autumn, persisting through winter, and continuing into spring, and it can be found in freezing weather when almost nothing else is out. Fruit bodies are typically scattered or in small groups of two or three along a branch, sometimes in a loose row where the mycelium follows a crack in the bark.

Separating it from the look-alikes

Lentinus arcularius is the summer counterpart. It has notably larger, strongly elongated and angular pores, usually one to two per millimetre or coarser, a more conspicuously and persistently hairy cap margin, and it fruits from late spring through summer. Pore size and season together separate the two in most cases.

Lentinus substrictus is very close and mainly a spring species, with a paler, often more ochre cap, a finer pore surface and a more slender stature; some collections are genuinely difficult and separation may rest on microscopy and fruiting time.

Cerioporus varius has a smooth, shiny, ochre to tan cap and, decisively, a stipe with a sharply defined black lower half or black base, and its pores are even finer.

Picipes badius is larger, with a shiny, often chestnut to dark red-brown cap that can be broadly funnel-shaped and wavy, and a distinctly black, velvety lower stipe.

Cerioporus squamosus is far larger, with a conspicuously scaly ochre cap and a very short blackish lateral stem.

Ordinary gilled mushrooms are eliminated instantly by turning the fruit body over: the presence of pores rather than gills settles the question, and the leathery texture confirms it.

Quick field checklist

Small stalked polypore, dull brown velvety cap becoming dished, whitish fine pores at two to four per millimetre running slightly down the stem, a fringed margin when young, a tough leathery non-blackening stipe, on dead broadleaved branches, fruiting through the cold months, white spore print.