What’s all the stink about?

© Jennifer Kerekes
Original publication: Mycena News, November 2010

Clathrus
A Clathrus chrysomycelinus stinkhorn collected in Panama.
Photo © Jennifer Kerekes.

Stinkhorn fungi are known for their foul-smelling odors and remarkable morphologies. Taxonomically, the stinkhorns are currently placed in the gomphoid-phalloid clade in the new subclass Phallomycetidae (Hosaka et al., 2006), along with earthstars, cannonball fungi, coral fungi, club fungi, tooth fungi, false truffles and even some gilled fungi and resupinate fungi. This gomphoid-phalloid clade is both morphologically and ecologically diverse. Prior to the recent reclassification, two families of stinkhorns were recognized, the Phallaceae family, consisting of those with unbranched stems and including species of Phallus, Mutinus and Dictyophora, and the Clathraceae family, consisting of those with branched stems and latticed structures, such as Clathrus, Lysurus, Colus and Laterna.

However, in Hosaka et al., it appears that both families, Phallaceae and Clathraceae, hold up, except that Lysurus is in the family Lysuraceae. These three families and three other families, make up the order Phallales.  

Stinkhorn fungi are most notable for their repugnant odors. This odor, which has been characterized as “obnoxious,” “cadaverous,” “putrid” and like “rotting carrion,” helps attract flies and other insects and thus aids the fungus in spore dispersal.

Clathrus
Clathrus archeri from California. Photo © Michael Wood.

The insects consume the fungal spores and the gleba, and the spores then germinate once they have passed through the digestive system of the insects. A chemical analysis performed on the gelatinous layer of Clathrus eggs revealed it to be rich in potassium, calcium, manganese and iron (Stijve, 1997). It appears that some stinkhorns concentrate manganese and have much higher concentrations of manganese and iron than other fungi. The author suggests that manganese plays a role in the enzymatic breakdown of the gleba and notes a release of carbon dioxide with the formation of the carrion-like odor. The increase in calcium appears to play a role in stabilizing the gelatinous layer that protects the fruiting body during the growth of the egg. Sapromyiophily – the attraction of flies through mimicry of their food and brood sites (Johnson and Jurgens, 2010) - also occurs, and perhaps is most well-known, in angiosperms and certain mosses. Amorphophallus, Rafflesia and Stapelia are well known carrion flowers that attract flies and other insects to aid in pollen dispersal. A recent study by Marino, Raguso and Goffinet in 2009 reported that sapromyiophily occurs in some species of mosses in the family Splachnaceae. Flies are attracted to the odors produced by the moss sporophyte and aid in spore dispersal.  

In a study published this year, Johnson and Jurgens investigated how closely the scent chemistries of a stinkhorn fungus and a carrion flower compared with the scent chemistries of carrion and feces. They studied the scent chemistries of the stinkhorn fungus Clathrus archeri, the octopus stinkhorn, and seven fly-pollinated plant species and scent samples collected from rotting meat, a rat carcass and horse and dog feces. They found compounds typical of carrion, such as oligosulphides, and of feces, such as phenol, indole and pcresol, present in the scents of the stinkhorn fungus and carrion flowers. Twenty-two compounds were found in C. archeri consisting of mostly aliphatic compounds and alcohols, along with benzenoids, phenylpropanoids, nitrogen-containing compounds and Sulphur containing compounds. The C. archeri scent profile fell between that of the carrion samples and the fecal samples. The similarity of the scent profiles confirms that both the fungus and the angiosperms are mimics of fly food sources. This study also showed that there is convergence across kingdoms of odorous fly attractants.  

Phallus
Phallus hadriani from California. Photo © Fred Stevens.

Ecologically, stinkhorns are saprotrophs and are not as common as other types of fungi. Often, the fruiting bodies can be spontaneous and ephemeral. There are a number of reports of stinkhorns being introduced. A well-documented example of a stinkhorn that has been introduced and spread is Clathrus archeri. It was introduced to Europe around 1920, possibly from wool imports from Australia, and then spread throughout Europe (Daisie, 2009).

Although repugnant in smell, stinkhorns are always a treasure and a surprise to find in the field! Or, to others, collecting stinkhorns could be approached as a sport, like Aunt Eddy did in the book Period Piece: “Armed with a basket and a pointed stick, and wearing a special hunting cloak and gloves, she would sniff her way round the wood, pausing here and there, her nostrils twitching, when she caught a whiff of her prey; then at last, with a deadly pounce, she would fall upon her victim, and poke his putrid carcass into her basket.”

Additional information:

Literature Cited:

About the Author:
Jennifer Kerekes received a Ph.D. in Microbiology in December, 2011 from the University of California at Berkeley, where she worked with Dr.Tom Bruns. She is interested in the ecology and diversity of saprotrophic fungal communities.