Umbrella Polypore Identification Guide

The find and the setting

The Umbrella Polypore announces itself as a mass rather than a mushroom. You are walking in mature broadleaved woodland, usually near the base of an oak, beech or maple, or beside an old stump or a buried root, and there is a pale grey-brown mound on the ground that at a distance looks like a heap of small pebbles or a cauliflower head. Close up it resolves into a single fleshy trunk that rises from the soil, branches repeatedly, and ends in dozens of small, separate, circular caps.

The whole cluster commonly measures 15 to 40 cm across and can exceed half a metre in exceptional specimens. Cap count typically runs from thirty to well over a hundred. It is always attached at one point and always arises from soil or leaf litter rather than perched directly on the side of a log, because the connection to the wood is underground.

Reading the individual caps

Isolate one cap at the edge of the cluster and examine it on its own, because this is where the identification is made. Each cap is small, 1 to 4 cm across, and circular or nearly so, with an even margin that is often slightly inrolled when young and flattens or waves with age.

The critical feature is the attachment. Each cap sits on its own slender stalk, and that stalk joins the cap in the middle of its underside, not at one edge. Look at the upper surface and you should see a small central dimple or navel over the point of attachment, so a mature cap is shallowly funnel-shaped or umbilicate. Circular caps with central stalks is the character that separates this fungus from every superficially similar cluster fungus.

The upper surface is dry, smooth to minutely fibrillose or finely scurfy, and coloured pale greyish-brown, tan, buff or dull ochre, often a little darker toward the centre. It is not brightly coloured, not conspicuously scaly, and not zoned into contrasting bands.

The pore surface and the branching trunk

Turn a cap over. The spore-bearing surface consists of pores, not gills, and they are white to cream, small and angular, roughly 1 to 3 per millimetre in fresh material. They become slightly larger and more angular toward the stalk.

Follow the pore surface inward with your eye. It runs down onto the stalk for a short distance, so the tube layer is decurrent, and the fine white pore texture continues visibly onto the upper part of each little stem. Since the caps are crowded, this creates a lacy white surface across the underside of the whole cluster.

Now trace the branching. Below the caps the stalks merge into progressively thicker branches, and those merge into a single stout, whitish to buff trunk at ground level. The branch system is repeatedly and irregularly divided, with the caps concentrated on the outer surface of the mound.

Base, flesh and section

Excavate the base carefully with a knife or trowel. Below the trunk you should find that the fungus arises from a hard, dark, tuber-like underground body called a sclerotium, roughly the size and shape of a potato and often blackish outside and pale inside, attached to buried roots or rotting wood. That structure is a strong confirmation, although it is not always easy to find and may be well below the litter.

Slice through a cap and its stalk. The flesh is white and remains white; it is soft and slightly fibrous in the caps and progressively tougher and more elastic down in the branches and trunk. It does not stain black, blue, red or brown when cut or bruised, though very old clusters yellow and then brown as they dry out and collapse. There is no gelatinous layer, no latex and no distinct dark line in section. Fresh material has a mild, pleasant, faintly earthy odour.

Spore print and season

To take a print, cut off one or two caps and lay them pore-side down on black or dark grey paper, since the print is white and will vanish on a white sheet. Cover the caps with a bowl and leave them three to six hours in a cool spot; polypore prints are often thin, so give it time and use several caps.

The print is white. Under the microscope the spores are smooth, thin-walled and cylindrical to narrowly ellipsoid, approximately 7 to 10 by 3 to 4 micrometres, with a slight apical taper. The hyphal system is dimitic, with tough skeletal hyphae running through the branches, which explains why the trunk is far more leathery than the tender caps.

Fruiting runs mostly from early summer through to early autumn, with the strongest showing after prolonged warm rain. Individual clusters last only a week or two before insects and rot break them down, but the underground sclerotium persists, and a site that produces one year will frequently produce again in the same spot for many seasons.

Substrate and ecology

Polyporus umbellatus lives on the roots and stumps of broadleaved trees. Oak is the most frequently cited host, with beech, maple, birch, hornbeam and elm also recorded. It behaves as a weak parasite and root-rot organism on living or declining trees and as a saprotroph on dead root systems, causing a white rot in which lignin is degraded and the residual wood becomes pale and fibrous.

Because the attachment is underground, the fruit body appears to grow out of bare soil, which misleads people into searching for a terrestrial mushroom. Always look at the surroundings: a stump, a cut trunk, a leaning veteran tree or the remains of a felled hardwood is normally within a couple of metres. It is generally uncommon and patchily distributed, more frequent in old woodland with plenty of dead root material.

Separating it from its closest look-alikes

Grifola frondosa is the species most often confused with it and shares the habit of forming a large branched cluster at the foot of oaks. The difference is in the shape and attachment of the individual caps. In Grifola frondosa the caps are fan-shaped, tongue-shaped or spoon-shaped with a wavy margin, they are attached laterally or off-centre, and they overlap in dense rosettes so that individual caps are hard to separate. They are also typically larger, greyer to brownish, and often faintly zoned. Polyporus umbellatus keeps its caps circular, discrete, centrally stalked and dimpled.

Meripilus giganteus forms very large overlapping fans from a common base at the foot of beech and other hardwoods, but its caps are broad, laterally attached and lack central stalks, and the whole fruit body blackens conspicuously where it is bruised or handled, which this species never does.

Cerioporus squamosus produces a single or few large kidney-shaped caps with coarse dark scales and a thick black-based lateral stalk, rather than many small smooth circular caps on a branched trunk.

Bondarzewia berkeleyi is much larger and thicker-fleshed, with a few massive, pale, rough-surfaced fans and coarse decurrent pores, growing from stumps and roots of oak.

Sparassis species grow at conifer or oak bases and form a large clustered mass, but they consist of flattened, wavy, noodle-like lobes with a smooth fertile surface and no pores at all.