Honey Fungus Identification Guide

The Encounter

Honey fungus announces itself as a crowd. You round the base of an old beech or oak in autumn, or step up to a garden stump, and there is a dense clump of tawny mushrooms erupting from one point - thirty, sixty, sometimes over a hundred caps, stems packed together and splaying outward like a bunch of celery. The colour is warm: honey, tan, ochre, olive-brown, often with a paler yellowish rim and a distinctly darker centre.

The setting matters as much as the mushroom. Armillaria mellea fruits at the collar of standing broadleaf trees, on stumps, over buried roots, along fence lines where posts have rotted, and out of the lawn beside a tree that came down years ago. When it appears to grow from bare soil, it is drawing on wood you cannot see.

If a single specimen is standing alone, take it more slowly. The clustering habit is one of the best characters, and an isolated fruit body loses it.

The Cap, Step by Step

Take one mid-aged cap and work through it.

Size and shape. 3-15 cm across. Convex and rather domed at first, expanding to broadly convex and then flat, and in age often wavy or upturned at the rim with a shallow low umbo remaining at the centre.

Colour. Honey-yellow through tawny and ochre to olive-brown or tobacco, generally darkest over the middle and fading outwards. Colour is very variable and should never be the deciding character on its own - wet weather, age and light all shift it.

Surface. Dry to slightly greasy, not viscid. Over the central third, look with a lens for small, erect to recurved, darker fibrillose scales, most concentrated at the disc and thinning to nothing towards the edge. In young buttons these can make the cap look bristly; on old weathered caps they wash off entirely.

Margin. Even at first, becoming faintly striate with age as the gills show through, and sometimes hung with fine whitish veil fragments.

The Gills

Turn it over. The fungus has true gills, not tubes or spines, and their attachment is important.

They are adnate to slightly decurrent: they meet the stalk squarely and usually run a short distance down it. They are moderately crowded, fairly narrow, and interspersed with shorter gills that do not reach the stalk.

Colour begins white to cream and then dulls - pinkish-buff, pale tan, and finally with rusty or reddish-brown spotting, particularly along the edges and in older caps. That spotting is characteristic, and it can mislead people into thinking they have a brown-spored fungus. They do not, which brings us to the print.

The Ring and the Stipe

The stalk of Armillaria mellea is one of the most informative parts of the mushroom.

Length and shape. 5-15 cm long, 0.5-2 cm thick, usually tapering slightly downward or fused with its neighbours at the very base; fibrous, tough and stringy, so it tears lengthwise rather than snapping cleanly.

The ring. This is the key. There is a prominent, persistent, membranous ring high on the stalk, whitish and thick, often with a soft cottony texture and frequently edged or flecked with yellow woolly tufts on its underside. It is a real collar, not a faint fibrillose band, and it survives on most mature specimens.

Colour zones. Above the ring the stalk is whitish to pale cream, often finely floccose. Below the ring it darkens progressively downward through buff to tawny and brown, and the lower part is covered with fine fibrils or small scales.

The Base and What Lives Under the Bark

Do not stop at the soil line. Excavate the base of the clump, and peel a strip of bark off the wood alongside it.

Two things should turn up.

White mycelial sheets. Between the bark and the wood, and running up under the bark of a colonised trunk, the fungus builds flat, papery, white to creamy fan-shaped mycelial sheets. They are conspicuous, and they carry a strong fungal odour when freshly exposed.

Rhizomorphs. These are the famous bootlaces - cylindrical, dark brown to jet black, tough, string- or bootlace-like strands, 1-5 mm thick, running under the bark and out through the soil. Snap one and the interior is white. They are how the fungus travels metres of soil to reach the next root, and they are the single most convincing corroborating feature you can find. In a dark cavity, freshly grown mycelium may also glow faintly - the foxfire of old accounts.

Flesh and Colour Change

Cut a cap and stalk in half lengthwise. The flesh is white to pale cream, firm in the cap and markedly fibrous and stringy in the stalk. There is no latex and no dramatic staining; cut surfaces may slowly dull to buff or brownish, especially in the stalk base, but there is no blue, green or red flash.

Taking a Spore Print

This step is worth doing every time, because it separates Armillaria from most of its clustered wood-inhabiting look-alikes at a stroke.

Cut a mature cap free at the top of the stalk, set it gills-down on a sheet of black card - or on white paper with a strip of dark card underneath - cover it with a bowl, and leave it four hours to overnight in a cool place.

The deposit is white to very pale cream. It is never brown, never rusty, never purple-black. Under the microscope the spores are smooth, colourless, broadly ellipsoid, about 7-9 x 5-6 microns, and non-amyloid.

A practical tip: mature clusters shed heavily, so caps lower in a tier are often already dusted white by the caps above them. Look for that white bloom on the caps and on the surrounding leaf litter - it is a free spore print.

Substrate, Season and Ecology

Armillaria mellea is a root and butt pathogen and subsequent white-rot decayer of broadleaf trees, most typically oak, beech, birch, apple, privet and many garden shrubs. It infects living root systems, kills the cambium at the root collar, and then continues to decay the dead wood - so it is found on living trees in decline, on recently dead ones, and on stumps for years afterwards.

Fruiting is strongly seasonal: a concentrated autumn flush, usually after the first substantial cool rains, and typically finished by the first hard frosts. Individual colonies can be very large and very old, spreading by rhizomorph through soil to occupy a whole hedgerow or copse.

Look for the corroborating signs on the tree: thinning crown, dieback in the upper branches, resin or gum flow at the base on some hosts, loose bark at the collar, and a white stringy rot in the root wood.

Separating It From Its Look-alikes

Ringless honey fungus (Desarmillaria tabescens) is the closest match in colour, clustering habit and substrate - but it has no ring at all. Check the upper stalk carefully; if there is nothing but a slightly fibrillose surface, and the cap is dry and finely scaly and tawny, that is the ringless species.

Dark honey fungus (Armillaria ostoyae, also called A. solidipes) has a cap covered with distinctly dark brown to blackish scales and a thicker ring bearing dark brown scales on its underside, and it is strongly associated with conifers.

Bulbous honey fungus (Armillaria gallica) typically fruits in small groups rather than dense clumps, has a swollen, club-shaped or bulbous stalk base, sparse cap scales, and a thin, cobwebby, yellow-flecked ring that often vanishes.

Shaggy scalycap and its relatives (Pholiota squarrosa, P. aurivella) cluster on the same trunks and also have rings, but their gills turn rusty-brown and their spore print is rust to cinnamon-brown. P. squarrosa is covered in coarse upturned scales all over cap and stalk; P. aurivella has a slimy golden cap.

Sulphur tuft (Hypholoma fasciculare) clusters on stumps but is smaller, brighter sulphur-yellow, has no ring, has greenish-yellow gills that become purple-brown, and gives a purple-brown spore print.

Sheathed woodtuft (Kuehneromyces mutabilis) is a tight cluster on hardwood with a ring, but its cap is smooth and strongly two-toned as it dries out, its stalk below the ring is covered in dark recurved scales, its gills go cinnamon and its print is brown.

Funeral bell (Galerina marginata) grows in smaller clusters on wood, is smaller, has a smooth, hygrophanous, brownish cap with no scales, brown gills, and a rusty-brown spore print.

Velvet shank (Flammulina velutipes) is a winter species on elm and willow with an orange, viscid cap, no ring, and a dark velvety-brown lower stalk; its print is white, so use the ring and the stalk surface.

Big laughing gym (Gymnopilus junonius) forms large clusters at hardwood bases with a ring, but it is a stronger orange-rust throughout and drops a bright rusty-orange print.

In Short

Cluster on or beside broadleaf wood; honey to tawny cap with dark fibrillose central scales; adnate to slightly decurrent cream gills that rust-spot with age; a substantial white membranous ring with yellow flecking; fibrous stalk browning downward; black rhizomorphs and white mycelial sheets under the bark; and a white spore print. Get all seven and the identification is settled.