Common Stinkhorn Identification Guide

The find, and how it usually starts

You generally locate the Common Stinkhorn by nose long before you see it, then spend a minute triangulating. The setting is deciduous or mixed woodland with a deep leaf and humus layer, a garden bed heavy with old wood chips, a hedge bank, or the rotten remains of a buried stump. What eventually resolves out of the leaf litter is a white, hollow, spongy column ten to twenty-five centimetres tall, standing straight up like a candle, capped by a dark, olive-green, glistening thimble. Flies are usually crawling all over the head.

Look immediately at the ground around it. Phallus impudicus almost never occurs singly for long, and where one has emerged you will normally find partly buried white "eggs" nearby at various stages, plus the collapsed, hollow remains of earlier fruit bodies from the same week.

The egg stage, and why you should cut one

Half the identification of a stinkhorn lives in its immature stage. The egg is a whitish to pale buff, slightly translucent ball four to six centimetres across, sitting half-buried in the litter and attached at the base to a thick white mycelial cord, or rhizomorph, that can be traced back into the soil for a considerable distance. It feels soft and yielding, like a partly deflated rubber ball, quite unlike the hard, dense earthballs it can be mistaken for.

Cut an egg cleanly in half from top to bottom and read the layers from the outside in. There is a tough white outer skin (the peridium), then a thick, clear, jelly-like layer, then a compressed, folded structure at the centre that is already recognisably a miniature stinkhorn: a pale spongy stalk coiled below a small ridged cap smeared with dark olive-green tissue. Nothing else in the woodland produces that layered, gelatinous, pre-formed section, and it settles the identification on the spot.

The mature receptacle

When conditions are right the egg splits at the apex and the stalk elongates rapidly, sometimes within a few hours, by inflating its pre-formed cells rather than by growing new tissue.

Stipe. White to off-white, ten to twenty-five centimetres tall and two to four centimetres thick, cylindrical, tapering slightly at both ends, and hollow down the middle. The wall is built of a coarse, chambered, foam-like or spongy structure that you can see clearly in section. It is brittle rather than fibrous, and snaps rather than tears.

Head. A thimble-shaped or bell-shaped cap two to four and a half centimetres tall sits over the top of the stalk, attached only at the apex and hanging free below like a skirt of a candle-snuffer. Wipe or wash the head and you will find the surface is not smooth: it is deeply pitted and reticulate, a network of raised ridges enclosing irregular chambers, the whole thing whitish to pale cream underneath.

Gleba. Over that ridged surface sits the spore slime, a dark olive-green to blackish, glistening, thick mucilage. At the very top of the head is a small white ring or disc around a central perforation.

Base. At ground level the remains of the egg persist as a loose, white, sac-like volva enclosing the bottom of the stalk, with the rhizomorph still attached beneath it. Always dig for the volva; it is a required character.

Flesh, section and colour change

Cut a mature specimen lengthwise. The stipe wall is white, chambered and spongy throughout, with a wide hollow core; there is no fibrous flesh, no pith and no separate cortex. There is no bruising reaction, no latex and no blueing. The only dramatic change is the loss of the gleba: once insects have removed it, the head is left as a bare white or cream honeycombed cone, and at that stage many people fail to recognise a stinkhorn at all because the diagnostic green slime has gone.

Spores: why there is no print, and what to do instead

Phallus impudicus has no gills, pores or teeth, and it does not shed spores into the air. The spores are embedded in the slimy gleba, which is designed to be carried off on the bodies of insects, so setting a cap on paper achieves nothing.

If you want to see the spores, scrape a trace of the olive slime onto a slide with a blade tip and dilute it with water. Under a microscope the spores are numerous, very small, smooth, cylindrical to sausage-shaped and pale, which is quite unlike the ornamented spores of puffballs and earthballs.

For field purposes, record the gleba colour, its consistency, and the fact that it is being removed by insects rather than dropped.

Substrate, season and ecology

This is a saprotroph of woody debris and rich humus. Its mycelium colonises buried branches, root fragments, stumps, sawdust and heavily mulched garden soil, forming long white cords that run for metres and terminate in eggs. Broadleaf woodland, particularly beech and oak with deep leaf litter, is the classic habitat, but well-mulched shrub borders, hedge banks and old sawdust piles all produce it.

The season runs from early summer into late autumn, peaking after warm wet spells, and eggs can sit dormant in the litter for weeks waiting for the right conditions before shooting up in a morning.

The ecology is unusual and helps confirm the find. Instead of releasing spores to the wind, the fungus advertises to flies and beetles with odour and a dark glistening head. Insects gather on the slime, become coated in spores, and disperse them, which is why a fresh specimen is usually black with flies and why an unattended one is stripped bare within a day.

Separating it from look-alikes on morphology alone

Phallus hadriani. Extremely similar in build, but the egg and the resulting volva are flushed pink, lilac or purplish rather than pure white, and it is strongly associated with sand dunes and sandy soil.

Dog stinkhorns, Mutinus species. Much slimmer, typically a centimetre or less thick, with an orange, pink or red upper portion, and crucially with no separate hanging cap: the gleba is smeared directly onto the tapering tip of the stalk rather than onto a distinct reticulate thimble.

Netted stinkhorns, Phallus indusiatus and relatives. Carry a conspicuous lacy skirt or net that hangs down from beneath the cap, a structure entirely absent in Phallus impudicus.

Cage fungi and octopus stinkhorns, Clathrus species. Emerge from a similar egg with a volva, but expand into a lattice sphere or into separate red arms rather than a single straight stalk with a capped head.

Earthballs, Scleroderma species. Only confusable at the egg stage, and only until you cut. Earthballs are hard, with a thick warted ochre rind and a firm marbled interior; stinkhorn eggs are soft, white, with a jelly layer and a folded miniature fruit body inside.

Amanita buttons. Also enclosed in a veil at the egg stage, but a vertical cut shows differentiated tissue with a recognisable cap, gill plates and stalk, and no gelatinous layer or olive-green core.

Field checklist

White spongy hollow stalk; free-hanging pitted and ridged thimble cap; olive-green slime with a white apical disc; sac-like volva at the base; thick white rhizomorph; soft white eggs with a jelly layer nearby; deep humus or buried wood; summer to autumn. That set is Phallus impudicus.