Dog Stinkhorn Identification Guide

The First Impression and the Setting

Dog Stinkhorn usually announces itself before you see it. You are walking through damp deciduous woodland, or along a garden border that was mulched with bark two seasons ago, and you catch a thin, sweetish, faintly putrid smell that does not belong to leaf mould. Follow it and you find, pushing up out of leaf litter or wood chips, a slender orange-tipped spike three to twelve centimetres tall and barely a centimetre thick, standing alone or in a loose scatter of two or three. Flies are almost always involved: a fresh fruit body carries a small crawling congregation on its dark tip.

The overall impression is of something narrow, slightly curved, hollow and rather fragile, quite unlike the thick white column of the larger stinkhorns.

Working Down From the Tip

Start at the top. The apex is bluntly pointed and pierced by a small pore, and in fresh material it is coated for the upper two to four centimetres in gleba, the dark olive-green to olive-brown spore slime. This is a thin, glossy, sticky layer, and it is what the flies are working on. Given a few hours of insect attention the gleba is stripped away entirely, and what remains is the bare receptacle beneath, which is where the useful colour lives.

Once the slime has gone you see the true character of the fertile zone: a slender, tapering, spongy-surfaced orange to orange-red section that shades gradually, not abruptly, into the paler stalk below. The word to hold onto is "gradually". In Dog Stinkhorn the transition from orange top to whitish base is a soft gradient over a couple of centimetres, and the orange is a fairly restrained apricot to salmon-orange rather than a hot scarlet.

There is no distinct cap, no skirt, no lattice, and no ring. The fertile head is simply the top of the stalk, not a separate structure resting on it, and running a fingernail up the shaft confirms that there is no seam or overhang where a cap would attach. That single observation immediately removes the whole Phallus group from consideration.

The Stalk, the Base and the Egg

The stalk is hollow, cylindrical to very slightly tapered at both ends, and built of a spongy chambered tissue that looks like polystyrene foam under a lens. It is white to pale cream, sometimes with a faint pink or buff flush in the lower half, and brittle enough to snap rather than bend.

At ground level the stalk emerges from a persistent volva, the ruptured remains of the egg. It is a white to dirty-cream, slightly flabby sac two to three centimetres across, often two- or three-lobed at the mouth, and it usually stays half buried. Excavate around it gently with a finger and you should find one or more white cord-like rhizomorphs running away from the base into the litter, thin, tough, branching strands that connect the fruit body to the mycelium in the surrounding debris.

Immature specimens are worth cutting. An unopened egg is a smooth white to pale ochre ovoid, one to two centimetres, with the texture of a soft grape. Sliced vertically it shows, from the outside in, a thin white skin, a thick clear gelatinous layer, a compressed dark green band of immature gleba, and, coiled and folded in the middle, the miniature orange-tipped receptacle waiting to expand. That cross-section is one of the most decisive identifications available in the field, because nothing else in the litter is built like it.

Flesh, Texture and Colour Change

There is no colour change on cutting or bruising in the sense that a bolete or a Lactarius changes. The flesh of the stalk is white, unchanging, and produces no latex. What does change is the whole fruit body over time: the orange fades and the structure collapses. A stinkhorn expands from egg to full height in a few hours, holds itself upright for perhaps a day, and then wilts into a limp, discoloured, fly-blown stub.

Spores and Why the Print Is Different Here

Do not bother laying this species on paper overnight. Stinkhorns do not shed a dry spore print; their spores are packaged in slime and dispersed by insects that walk through it and carry it away on their feet and mouthparts. The equivalent procedure is to take a smear. Touch a cover slip or a slide to the dark tip, dilute the slime with a drop of water, and look at it under a microscope. You will see enormous numbers of small, smooth, cylindrical to narrowly ellipsoid, pale greenish spores roughly four to five micrometres long and one and a half to two micrometres wide. That extreme abundance of tiny cylindrical spores is characteristic of the whole stinkhorn group.

Substrate, Season and Habitat

Look in rich, moist, humus-heavy ground with plenty of buried wood: deciduous woodland with a deep litter layer, old hedge banks, shaded garden beds, and above all bark mulch and wood chip. It is a decomposer of woody debris, so the presence of rotting sticks, sawdust, chip mulch or an old stump within a metre or two is a supporting observation. Beech, oak, hazel and mixed broadleaf woodland are typical.

The season runs from midsummer through to late autumn, peaking after warm, wet spells.

Separating It From the Look-alikes

Mutinus ravenelii is the closest and the most frequently confused. It is stouter and shorter for its width, and the fertile head is a well-defined, swollen, rosy-pink to reddish-magenta zone that meets the white stalk along a fairly abrupt line, sometimes with a slight shoulder. Dog Stinkhorn is more slender, more orange than pink, and the colours blend into one another.

Mutinus elegans is larger, taller and more strongly tapered to a narrow point, with the gleba occupying the upper third to half of the fruit body and the exposed receptacle a deep orange to orange-red. Its whole outline is that of a long thin horn, whereas Dog Stinkhorn is closer to a slim cylinder with an orange cap of colour on top.

Phallus impudicus and Phallus hadriani are in a different size class altogether, ten to twenty-five centimetres tall and two to four centimetres thick, and both carry a genuinely separate, thimble-shaped, deeply pitted and ridged cap that hangs free from the top of a thick white stalk. Phallus hadriani additionally has a pinkish-violet volva and grows in sand dunes. If you can see a distinct honeycombed cap with a white perforated disc at its apex, it is not a Mutinus.

Unopened eggs can be mistaken for a puffball or an earthball, but the cut section settles it: only a stinkhorn shows a gelatinous jacket around a folded miniature receptacle.

A Working Field Sequence

Smell first, then look for flies. Confirm a slender unbranched spike under one centimetre thick with no separate cap. Wipe the tip and check for an orange, spongy, gradually shading fertile zone. Find the white lobed volva at the base and follow a rhizomorph into the litter. Look for wood chip or buried wood. Cut any nearby egg vertically to see the coiled orange tip in section.