Netted Stinkhorn Identification Guide

The First Impression

You usually smell the netted stinkhorn before you see it. Working through rich leaf litter in a hardwood woodland, or across a mulched garden bed on a humid summer morning, you catch a heavy, sweetish rotting odour and start scanning the ground. What you find is a pale, upright, spongy column 15 cm or so tall, capped by a dark olive-brown, slimy head that is usually covered in flies, and hanging from beneath that head, a short white lacy skirt.

That skirt, the indusium, is the character in the common name and the fastest route to identification in the field. Phallus duplicatus, long known as Dictyophora duplicata, is a stinkhorn of eastern North America and East Asia, occurring in deciduous woodland, along wooded edges, and very often in wood chips, garden beds and disturbed rich ground.

The Egg Stage

Half the specimens you find will still be underground or barely emergent. It is worth learning to read them.

The egg is 3 to 6 cm across, ovoid to obovoid or slightly irregular, white to pale pinkish buff or dirty cream, firm and slightly yielding to the touch. It sits partly buried, and it is anchored by a thick white cord, a rhizomorph, that runs off into the litter. Do not pull it up; excavate it, because the rhizomorph attachment is a useful confirming feature.

Cut a fresh egg vertically with a sharp knife. From the outside inward you should see: a thin, tough white outer skin; a thick, clear, gelatinous layer; a dark olive-brown to blackish band, which is the immature spore mass; and, inside that, the pale, chambered, folded tissue of the receptacle waiting to expand. In Phallus duplicatus you can also see the future indusium as a fine folded membrane wrapped around the young cap.

That cross-section rules out puffballs immediately, since a young puffball is uniformly white, solid and undifferentiated with no gelatinous layer and no preformed stalk.

The Expanded Fruit Body

Expansion is fast, usually overnight or in the early morning, and takes an hour or two.

Overall stature. Total height typically 12 to 20 cm. Everything about it is soft and short-lived; by afternoon a fruit body can already be sagging.

Stipe. The stalk, properly the receptacle, is 10 to 18 cm long and 2 to 4 cm thick, white to cream, tapering slightly at both ends, hollow, and built of a spongy network of chambers, so it is brittle and light. Snap a piece and the cut surface looks like a stiff white foam.

Volva. At the base a whitish to pinkish-tinged sac remains, the ruptured remnant of the egg, usually still holding the rhizomorph.

Cap. The head is 2.5 to 4.5 cm tall, conical to thimble- or bell-shaped, and it is attached to the stalk only at the very top, hanging free like a cover. The apex is a small, flattened, white disc pierced by a pore. When fresh the whole cap is coated in the gleba, a dark olive-brown to almost black slime. Once flies and rain have stripped that slime away, look at the surface beneath: it is coarsely reticulate, a raised network of ridges enclosing distinct pits. That reticulate cap surface is an important character.

Indusium. The white net hangs from beneath the cap margin. In this species it is comparatively short and coarse, usually reaching about a third to halfway down the stalk, with large, irregular, polygonal holes. It may flare outward like a crinoline or collapse against the stalk. Because it withers quickly, an afternoon find may show only a shrivelled ring of white tissue under the cap, so look carefully before concluding a skirt is absent.

Flesh and colour change. The stalk flesh is white and spongy and does not stain when cut. The gleba stains everything it touches olive-brown.

Odour. Strong, foetid, carrion-like, and detectable from several metres downwind. It fades once the gleba has been removed.

Spores, and Why There Is No Print

Stinkhorns do not drop a spore print. The spores are embedded in slime and are carried off by insects rather than released into the air, so the standard cap-on-paper method returns nothing.

Instead, scrape a trace of gleba onto a glass slide, add a drop of water and examine it. The spores are minute, roughly 3.5 to 4.5 by 1.5 to 2 micrometres, smooth, thin-walled, cylindrical to narrowly ellipsoid, and hyaline to pale olive individually even though the mass appears almost black. If you have no microscope, smear a little gleba across white card and rinse it: the wash leaves an olive-brown stain.

Substrate, Season and Ecology

The fungus is a decomposer of buried wood and rich organic matter. Look in humus-rich deciduous woodland, around old hardwood stumps, in mulched beds, wood chip paths and garden borders. It fruits from early summer into autumn, always after warm heavy rain, and it is often gregarious, appearing in loose groups or arcs where the mycelium has spread through the substrate.

Its ecology is written into its morphology: the odour and the sticky spore mass exist to recruit flies and beetles, which land on the gleba, feed, and carry spores away on their bodies. The lacy indusium is thought to give insects a landing platform and to make the fruit body more conspicuous.

Separating the Look-Alikes on Morphology

Phallus indusiatus. The other famous skirted stinkhorn. Its indusium is long, fine-meshed and delicate, reaching nearly to the ground and often touching the volva, and it is a tropical and subtropical species of bamboo and palm litter. P. duplicatus has a shorter, coarser, thicker skirt with larger holes.

Phallus impudicus. Similar size and shape with a reticulate cap, but it has no visible skirt; at most a hidden rudimentary veil under the cap that never hangs free.

Phallus ravenelii. Frequent on sawdust piles and wood debris in the same region. Its cap surface is granular or finely pebbled rather than coarsely ridged and pitted, and it lacks an indusium. Its eggs are often pinkish to purplish.

Phallus hadriani. Distinguished by a pinkish to violet egg and volva, a reticulate cap, no skirt, and a preference for sandy ground and dunes.

Mutinus species. Slimmer, with no separate cap at all: the gleba is smeared directly onto the tapering, often orange, pink or red upper part of the stalk. No skirt, no thimble-shaped cover.

Clathrus and Lysurus species. Emerge from similar eggs but expand into lattices, cages or clusters of arms rather than a plain stalk with a cap, so confusion is only possible at the egg stage.

The decisive field combination is: white spongy hollow stalk from a volva with a rooting cord, a free-hanging thimble-shaped cap with a white perforate apical disc and a coarsely reticulate surface under the olive-brown slime, and a short, coarse-meshed white net hanging from beneath the cap.