Dune Stinkhorn Identification Guide

The Setting and the First Impression

Habitat does more work here than in almost any other identification. Dune Stinkhorn is a sand specialist. You will be standing in a coastal dune system, most often in the fixed or semi-fixed dunes behind the foredune, among marram grass, sea buckthorn, creeping willow or the mossy turf of a dune slack. Inland records come from sandy heaths, sandy gardens, sand pits and river sands, but the classic setting is a dune ridge with bare blown sand between the grass tussocks.

The first impression is of a substantial white column standing proud of the sand, ten to twenty centimetres tall and two to four centimetres thick, with a dark, glistening, honeycombed head on top. As with all stinkhorns, the odour arrives before the sighting, a heavy, sweetish-putrid smell that carries on the wind, and there will usually be flies working the head.

Then look at the base, because that is where this species declares itself. Sitting in the sand at the foot of the stalk is a soft, sac-like volva flushed pink, lilac, rosy-violet or pale magenta. That coloured egg case is the diagnostic character of Dune Stinkhorn.

Reading the Head

The fertile head is a separate structure from the stalk, and confirming that is the first step. It is thimble- or bell-shaped, two to four centimetres tall, sitting over the top of the stem like a cap and free from it except at the apex, so you can slide a blade of grass up under its lower rim.

Its surface is deeply and irregularly pitted and ridged, a coarse honeycomb or brain-like reticulation of raised ribs enclosing angular chambers. In a fresh specimen those chambers are filled and the whole head is smeared with gleba, the dark olive-green to olive-brown spore slime, so the sculpture is masked and the head simply looks black-green and wet. Once flies have stripped the slime, the pale whitish to cream reticulate skeleton is exposed and the honeycomb pattern is obvious.

At the very apex sits a small white disc with a central perforation, flat or slightly domed, contrasting sharply with the dark gleba around it. That perforated apical disc is a good genus-level confirmation and is easy to see even on slime-covered material.

The Stalk, the Volva and the Rhizomorph

The stalk is white to very pale cream, cylindrical, tapering slightly towards both ends, and hollow. Its wall is built of spongy, chambered, foam-like tissue that looks under a lens like a fine honeycomb in cross-section.

Follow it down. The volva at the base is two to five centimetres across, ovoid to slightly flattened, and soft. The colour ranges from a pale rosy flush to a distinct pinkish-lilac or violaceous tint, strongest on the outer skin and often deepest where the sand has been in contact with it. Weather bleaches it, so read the character on fresh material and, ideally, on an unopened egg.

Dig carefully. Below the volva runs a stout white rhizomorph, a tough cord-like strand of bundled hyphae, often ten to thirty centimetres long, that anchors the fruit body deep in the sand and links it to the buried mycelium among grass roots and sand-bound organic matter.

The Egg and What It Shows in Section

The best identification is made on an unopened egg. It is a firm, smooth, ovoid body three to five centimetres across, whitish flushed with pink or violet, half buried and easily missed among the marram roots.

Cut it vertically. From outside in you will see: a thin skin carrying the pink to lilac pigment; a thick, clear, gelatinous layer, sometimes a centimetre deep; a dark olive-green band of immature gleba; and, folded and compressed in the middle, the miniature white receptacle and honeycombed head waiting to elongate. No other sand-dune fungus is built this way.

Flesh, Colour Change and Odour

The stalk flesh is white, spongy and unchanging; it does not blue, redden or exude latex on cutting. The gelatinous layer of the egg is clear to faintly pinkish and does not stain. The only real colour change in the life of the fruit body is the loss of the dark gleba as flies remove it, revealing the pale head beneath, and the general collapse and browning of the whole structure within a day or two.

The odour is strong, sweetish and carrion-like at maturity, and it is the reason flies gather.

Spores and Why a Print Is Not the Method

Stinkhorns do not shed a dry print, because their spores are embedded in slime and carried away by insects rather than falling on air currents. To examine them, touch a slide to the gleba, add a drop of water and a cover slip. Under the microscope you will find vast numbers of very small, smooth, cylindrical to narrowly ellipsoid, pale greenish-yellow spores, roughly three and a half to four and a half micrometres long by one and a half to two wide, floating in disintegrating slime.

Season and Ecology

Fruiting runs from late spring through summer into autumn, with the strongest flushes after warm, wet spells, and dune populations often fruit earlier in the year than woodland stinkhorns. The mycelium is a decomposer of buried organic matter in sand: root litter of marram and other dune grasses, buried leaves, and humus accumulating in fixed dune soils. Because dune systems are stable over decades, colonies persist and re-fruit in the same hollows year after year.

Separating It From Its Look-alikes on Morphology

Phallus impudicus is the species that matters. It is very similar in size, shape, sculpture and odour, and the reliable morphological separation is the volva: white, cream, or greyish in impudicus, and pink to lilac or violaceous in hadriani. Supporting differences are that impudicus is a woodland species tied to buried wood, stumps and rich leaf litter, that its egg is typically shallower in the ground with a shorter rhizomorph, and that hadriani is on average a little more slender with a slightly narrower head. Where the volva has faded, habitat and rhizomorph depth carry the identification.

Mutinus caninus and its relatives are far smaller and, decisively, have no separate cap at all: the slime is applied directly to a slender orange or pink tapering tip that is simply the top of the stalk, and the whole fruit body is barely a centimetre thick, with a plain white volva.

Phallus rubicundus has a pinkish to red stalk and a much smaller, less coarsely pitted head, and the veiled tropical stinkhorns hang a conspicuous net-like skirt from beneath the head, which Dune Stinkhorn never does. Clathrus and Lysurus species produce a latticed or arm-bearing receptacle with no stalk-and-cap structure at all.

A Working Field Sequence

Confirm the dune or sandy habitat. Note a stout white hollow stalk over ten centimetres tall. Confirm a separate thimble-shaped head with a coarse honeycomb sculpture and a white perforated apical disc. Excavate the base and read the volva colour for pink, lilac or violet. Follow the rhizomorph down through the sand. If eggs are present, cut one vertically and check for a pigmented skin over a clear gelatinous layer.