Phallus impudicus, known colloquially as the common stinkhorn, is a widespread fungus recognizable for its foul odor and its phallic shape when mature, the latter feature giving rise to several names in 17th-century England. It is a common mushroom in Europe and North America, where it occurs in habitats rich in wood debris such as forests and mulched gardens. It appears from summer to late autumn. The fruiting structure is tall and white with a slimy, dark olive colored conical head. Known as the gleba, this material contains the spores, and is transported by insects which are attracted by the odor—described as resembling carrion. Despite its foul smell, it is not poisonous and immature mushrooms are consumed in parts of France and Germany.
Description & appearance
Sometimes called the witch's egg, the immature stinkhorn is whitish or pinkish, egg-shaped, and typically 4 to 6 cm (1.6 to 2.4 in) by 3 to 5 cm (1.2 to 2.0 in). An immature fruiting body ("egg") in longitudinal section
On the outside is a thick whitish volva, also known as the peridium, covering the olive-colored gelatinous gleba. It is the latter that contains the spores and later stinks and attracts the flies; within this layer is a green layer which will become the 'head' of the expanded fruit body; and inside this is a white structure called the receptaculum (the stalk when expanded), that is hard, but has an airy structure like a sponge. The eggs become fully grown stinkhorns very rapidly, over a day or two. The mature stinkhorn is 10 to 30 cm (3.9 to 11.8 in) tall and 4 to 5 cm (1.6 to 2.0 in) in diameter, topped with a conical cap 2 to 4 cm (0.8 to 1.6 in) high that is covered with the greenish-brown slimy gleba. In older fungi the slime is eventually removed, exposing a bare yellowish pitted and ridged (reticulate) surface. This has a passing resemblance to the common morel (Morchella esculenta), for which it is sometimes mistaken.[8] The rate of growth of Phallus impudicus has been measured at 10–15 cm (4–6 in) per hour. The growing fruit body is able to exert up to 1.33 kPa of pressure — a force sufficient to push up through asphalt. The spores have an elliptical to oblong shape, with dimensions of 3–5 to 1.5–2.5 µm.
In North America, Phallus impudicus can be distinguished from the very similar P. hadriani by the latter's purplish-tinted volva. The dispersal of spores is different from most "typical" mushrooms that spread their spores through the air. Stinkhorns instead produce a sticky spore mass on their tip which has a sharp, sickly-sweet odor of carrion to attract flies and other insects. Odorous chemicals in the gleba include methanethiol, hydrogen sulfide, linalool, trans-ocimene, phenylacetaldehyde, dimethyl sulfide, and dimethyl trisulfide. The latter compound has been found to be emitted from fungating cancerous wounds. The mature fruiting bodies can be smelled from a considerable distance in the woods, and at close quarters most people find the cloying stink extremely repulsive. The flies land in the gleba and in doing so collect the spore mass on their legs and carry it to other locations. An Austrian study demonstrated that blow-flies (species Calliphora vicina, Lucilia caesar, Lucilia ampullacea and Dryomyza anilis) also feed on the slime, and soon after leaving the fruit body, they deposit liquid feces that contain a dense suspension of spores. The study also showed that beetles (Oeceoptoma thoracica and Meligethes viridescens) are attracted to the fungus, but seem to have less of a role in spore dispersal as they tend to feed on the hyphal tissue of the fruiting body.
There is also a possible ecological association between the P. impudicus and badger (Meles meles) setts. Fruiting bodies are commonly clustered in a zone 24 to 39 metres (79 to 128 ft) from the entrances; the setts typically harbor a regularly-available supply of badger cadavers – the mortality rate of cubs is high, and death is more likely to occur within the sett. The fruiting of large numbers of stinkhorns attracts a high population of blowflies (Calliphora and Lucilla breed on carrion); this ensures the rapid elimination of badger carcasses, removing a potential source of disease to the badger colony. The laxative effect of the gleba reduces the distance from the fruiting body to where the spores are deposited, ensuring the continued production of high densities of stinkhorns.
Distribution & habitat
The common stinkhorn can be found throughout much of Europe and North America, and it has also been collected in Asia (including China, Taiwan, and India), Costa Rica, Iceland, Tanzania, and southeast Australia. In North America, it is most common west of the Mississippi River; Ravenel's stinkhorn (Phallus ravenelii) is more common to the east. The fungus is associated with rotting wood, and as such it is most commonly encountered in deciduous woods where it fruits from summer to late autumn, though it may also be found in conifer woods or even grassy areas such as parks and gardens. It may also form mycorrhizal associations with certain trees.