Anemone Stinkhorn Identification Guide

The moment you spot it

Aseroe rubra does not ease you into an identification. One second you are looking at a bed of dark bark mulch, the next there is a flat scarlet star sitting on it, four to eight centimetres across, with a glistening blackish smear in the middle. The colour is closer to a poppy or a tomato skin than to anything else in the fungal world, and because the whole structure lies almost flat against the ground, the first impression is of something marine that has been dropped into a garden by mistake. That reaction is exactly why the fungus carries the name it does: the radiating arms genuinely do read as the tentacles of a sea anemone.

Before you kneel down, register the setting. This species is overwhelmingly a fungus of disturbed, wood-rich ground rather than deep natural forest. Landscaped beds, nursery stock, woodchipped paths, the mulched skirt around ornamental shrubs, sawdust piles and the ragged edges of car parks are the classic places. It arrived in many parts of the world as a hitch-hiker in horticultural material, so a colony often appears suddenly in a garden that has just been re-mulched and then persists there for years.

Start below ground with the egg

A proper identification starts with the stage most people walk past. Before it opens, Aseroe rubra is a whitish to pale pinkish-buff egg, roughly ovoid, one to three centimetres across, half buried in the mulch. Sift the surface litter with your fingers around any open specimen and you will usually turn up two or three of these at different stages of development. Each egg is anchored by a tough white cord of mycelium, a rhizomorph, that runs away through the substrate.

Slice an egg vertically with a sharp knife and the internal architecture explains everything about the mature fungus. Under the outer skin sits a thick, clear, gelatinous layer. Inside that lies the folded, compressed embryo of the receptacle, with the arms packed against one another like the ribs of a closed umbrella, and a dark olive-brown band marking the future spore slime. This gelatinous layer works as a water reservoir and as a lubricant; when the egg is ready, the stalk elongates in a matter of hours and pushes the star out through a ruptured opening, leaving the remains of the egg as a soft white cup, or volva, at the base.

Reading the arms

The open fruitbody has a short, hollow, spongy stalk, typically one to four centimetres high, whitish to pale pink or faintly orange, chambered inside like a piece of foam. At its top the stalk flares into a shallow disc, and from the rim of that disc six to ten arms radiate outwards.

The single most diagnostic detail is that each arm forks. Look closely and you will see that the arms are not simple rays but paired tips, splitting once for most of their length so that a specimen with, say, seven bases appears to have fourteen points. The arms are bright red to scarlet or crimson, sometimes shading to orange or pinkish toward the base, tapering, slightly channelled on the upper surface and often wrinkled or roughened below. They usually spread flat or curve down to touch the ground, and older arms become limp and collapse inwards.

The central disc and its spore slime

At the centre of the star, on and just around the disc, sits a dark olive-brown to blackish, shining, semi-liquid mass. This is the gleba, and it is where the spores are produced. Fresh, it is sticky and glossy, and it carries a powerful carrion odour. Flies find it within minutes of the star opening, and on a warm morning you can often locate a colony by watching where blowflies and small beetles are congregating rather than by looking at the ground.

That insect traffic is the whole point. Instead of dropping dry spores into moving air, this fungus wraps them in a scented slime, insects walk in it and fly off, and the spores travel in and on the insect. Within a day or two the gleba is stripped away, leaving the bare disc exposed as a pale, sometimes reddish plate with a small central depression. A cleaned specimen is much harder to recognise, so if the middle looks empty, check for stray dark residue in the grooves of the disc.

Stalk, base and flesh

Cut a mature specimen down the middle. The stalk wall is a single layer of white to pinkish, chambered, brittle tissue, and it snaps rather than tears. There is no ring, no true cap and no gill tissue anywhere. At ground level the split egg persists as a whitish, membranous, often muddy sac clinging around the stalk base, with the rhizomorph attached beneath. Neither the arms nor the stalk change colour when cut or bruised; they simply soften and darken as they decay, and the whole fruitbody collapses to a slimy red-brown smudge within one to two days.

What to do about a spore print

A conventional spore print is not how this species is confirmed. There are no gills or pores to shed a dry deposit, and the spores are held in the slime. Instead, take a pinhead of the gleba on the tip of a knife, smear it on a slide or a scrap of white card and let it dry: with a hand lens you can see a smooth brown film, and under a microscope the spores are very small, narrowly cylindrical to elliptical, smooth and pale olive-brown, roughly five to seven micrometres long. If you want a keepsake record, the disc of a cleaned specimen pressed on paper leaves a faint brownish ghost, but the reliable field characters are the fork-tipped red arms and the dark central disc.

Substrate and season

This is a saprotroph of wood in an advanced state of breakdown. It fruits directly from bark chips, sawdust, decaying mulch, compost, straw-rich beds and occasionally from lawn thatch over buried woody debris. It does not associate with living tree roots and it is not a wood decayer of standing timber. Fruiting follows warm, wet spells, so in warm-temperate and subtropical regions it can appear almost year-round after rain, while in cooler climates it is a phenomenon of late summer and autumn. Colonies are typically gregarious, with eggs, half-opened stars and collapsed remains all present in the same square metre.

Separating it from its closest relatives

The genuinely confusable fungi are other members of the stinkhorn family that produce arms rather than a capped column.

Clathrus archeri, the octopus stinkhorn, is the main one. Its arms are usually four to eight, they are thicker and taper more strongly, they are pitted or wrinkled with darker glebal patches spread along their inner surfaces rather than confined to a central disc, and critically they are joined at the tips when they first emerge and are not forked. There is also no distinct pale stalk lifting a flat disc; the arms rise more or less directly from the volva.

Lysurus mokusin has a conspicuously ribbed, angular, columnar stalk that is square or pentagonal in cross-section, topped by short arms that stay pressed together in a cluster rather than spreading into a flat star.

Clathrus ruber is a hollow red lattice, a closed cage of anastomosing arms with the gleba on the inside of the meshwork, and cannot be mistaken once seen.

Phallus and Mutinus species share the white egg and the dark slime but produce a single unbranched column with the gleba on a terminal cap or apex, with no arms at all.

Finally, remember that a very old, blackened, collapsed Aseroe can look like almost anything. When in doubt, dig for the eggs; a sliced egg showing a compressed ring of red arm tips around a dark glebal band settles the question straight away.

Quick field checklist

Flat red star lying on mulch; six to ten arms, each splitting into two tips; short hollow pale stalk; dark olive-brown slime on a central disc; white sac at ground level with a cord running into the substrate; woodchip or compost substrate; strong carrion odour with flies in attendance.