Veiled Polypore Identification Guide

The Scene and the First Impression

Veiled Polypore is a spring fungus of dead conifers, and the setting is very specific: a stand of pine, Douglas-fir, true fir, spruce or hemlock in which some trees died within the last year or two, usually after bark beetle attack, and still hold their bark. Look at standing dead trunks and at recently fallen logs. When the species fruits it fruits in numbers, sometimes dozens of small knobs studding a single trunk from the base to well above head height, all at the same stage.

The first impression is odd, because it does not read as a polypore at all. What you see is a small, smooth, chestnut to tan, rounded or hoof-shaped lump, 1.5 to 5 cm across and often nearly as deep, glued flat against the bark, with a slightly varnished or waxy sheen. It looks more like a gall, a resin blister or a small hard fruit than a bracket fungus, because the whole underside is sealed shut.

Reading the Outside

Handle one. The fruit body is surprisingly light, dry and corky-tough, and it detaches from the bark cleanly with a firm push.

The upper surface is smooth, glabrous, and coloured ochre, tan, cinnamon or chestnut-brown, usually paler when young and darker with age, sometimes with a thin resinous crust that shines in the light. There are no obvious concentric zones or ridges. The outline is globose, kidney-shaped or shortly hoof-shaped, sessile, attached over a narrow to moderately broad area of bark.

Then turn it over. This is where the identification is made. Instead of an open pore surface you find a continuous, tough, whitish to pale buff membrane, thick and slightly rubbery, completely enclosing the underside and forming a sealed chamber. That membrane is the veil the species is named for, a distinctive structure that no other polypore in the region produces.

On mature fruit bodies there is a single small aperture, roughly circular to irregular, usually near the base or lower margin, often enlarged and ragged where insects have chewed it. Young fruit bodies are completely closed with no opening at all. Beetles and other small insects crawl in through this hole and out again, and they leave carrying spores.

Cutting It Open

The fastest confirmation is a vertical cut through the middle with a stout knife.

The section shows, from the top down: a thin darker crust, a layer of white to pale buff corky flesh a few millimetres thick, then a layer of tubes hanging downward, and then an empty chamber walled off by the veil. Seeing the tube layer suspended inside a closed cavity is unlike anything else you will cut open.

The pore surface itself is white to cream when young, ageing buff, pinkish-tan and finally brown. Pores are small and round, about 3 to 5 per millimetre, and the tube layer is 1 to 4 mm deep. The flesh is white to pale buff, tough and corky, and does not change colour when cut. The odour is faint and slightly resinous or aromatic, in keeping with the conifer substrate.

Spores and How to Get a Print

An intact fruit body will not give a print, for the obvious reason that the pores are enclosed. To obtain one, slice the veil away cleanly with a scalpel to expose the tube mouths, then rest the exposed face over white paper in a humid chamber overnight. Fresh material deposits white. Note that this species does not rely on air dispersal at all in nature, so a poor print does not mean poor material.

Under the microscope the spores are smooth, thin-walled, hyaline and cylindrical to narrowly ellipsoid, roughly 9 to 13 by 4 to 5 micrometres, with a slightly flattened side.

Substrate, Season and Ecology

The substrate is the sapwood of recently killed conifers with the bark still attached, and the association with bark beetles is close enough to be a search strategy in itself. Beetles bore into a stressed or dying tree, the fungus establishes in the sapwood, and within a year the trunk produces a crop of sealed fruit bodies. In practice this means the best trees are those that died last season and still have red or fading needles or have just dropped them.

Fruiting is annual and concentrated in spring and early summer, though old blackened fruit bodies from previous years persist on the same trunks for a long time and are often the first sign that a tree is worth checking.

The ecology is genuinely unusual. Because the hymenium is sealed, spore release is not driven by wind. Insects entering and leaving through the aperture pick up spores and carry them to freshly beetle-attacked trees, and the fungus effectively hitchhikes on the same insects that create its habitat. The veil also keeps the chamber humid, which allows the fungus to sporulate through dry spells that would shut down an exposed bracket.

Distinguishing It from Everything Else

The enclosed pore surface is close to unique, so most look-alikes only trouble you at a distance or in poor material.

Fomitopsis pinicola, seen young, can be a similar brown lump on conifer wood, but its pore surface is open, white and exposed from the start, its crust is resinous and often banded red, orange and black, and it is perennial, growing over successive years into a large hoof.

Ganoderma species, Polyporus species and other brackets all present open pores.

Puffballs growing on wood, such as the pear-shaped Lycoperdon of stumps, can look like brown knobs at a glance, but they have soft, granular or spiny surfaces, an apical opening at the top rather than a lateral aperture near the base, and cutting one reveals a solid white then powdery interior with no tube layer.

Resin blisters, insect galls and pitch tubes on beetle-attacked bark are the commonest false positives on a first survey; they are hard, sticky and structureless, and one cut settles it.

Very young Veiled Polypore fruit bodies, still fully sealed with no aperture, are the trickiest of all, since they truly look like smooth galls. Check the substrate, check that the lump sits on bark rather than growing out of it, and cut one open. The white corky flesh over a hanging tube layer inside a closed chamber cannot be mistaken for anything else.