Busting the “No Known Poisonous Polypores” Myth: Hapalopilus nidulans

The cap of Hapalopilus nidulans starts out finely tomentose
but becomes glabrous with age.

I don’t know how many times I’ve read this phrase over the past couple of years: “There are no known poisonous polypores.” I see it mostly on internet forums, and mostly on threads about edible or medicinal fungi. Someone will excitedly post a photo of their first “chicken of the woods” (Laetiporus sp.) or “reishi” (Ganoderma sp.), photos that regularly, and clearly, show that the poster has got the wrong ID. This happens unbelievably frequently with the fad medicinal, “chaga” (Inonotus obliquus). A photo of a burl or gall, growing on the trunk of a tree that is obviously not a Betulina of any sort, will be posted as “chaga” and everyone will chime in their congratulations and suggest that the finder immediately race back to hack away at a living tree with a hatchet to claim his or her "prize." When someone sensible suggests that one of the above IDs may be flawed, another poster will jump in with the claim that a misidentification doesn’t matter anyway since “there are no known poisonous polypores.”

Well, it’s not true. There is at least one seriously toxic polypore, Hapalopilus nidulans (H. rutilans).  

Hapalopilus nidulans can be overlooked since it's often
quite small and frequently grows alone.

H. nidulans is an unassuming, cinnamon-coloured polypore that can grow up to 10 cm wide, though it's usually considerably smaller. It has a rough or smooth cap and small angular pores, 2-4 per millimetre. When fresh, its flesh is soft and watery; when dry it's tough and hard and can be quite brittle. A white rot agent, it prefers a wide variety of deciduous trees, but can occasionally be found on conifers. Though it's widely distributed east of the Rockies, it's not particularly common. 

The small, angular pores of Hapalopilus nidulans

An Impressive Chemical Reaction

Basically, it's an easily overlooked, unexciting fungus—unless you happen to have some KOH handy, or a bottle of ammonia tucked under your kitchen sink. Personally, I loathe the smell of ammonia, probably because I once had a 19-year-old cat that could no longer find its box. Though that cat is long dead, I still put up with the stink of ammonia since this inexpensive cleaning solution is a wonderful tool for any fungiphile as many species of bolete undergo specific colour changes when hit with a drop of it—as does H. nidulans.

When this otherwise boring fungus comes into contact with either ammonia or KOH, it immediately turns a psychedelic fuchsia (or cherry red in other parts of the world), a reaction that's so magical and so spectacular it's hard not to play with the effect over and over again. At least it is for me. It's also a fabulous part of anyone's arsenal of ultra-cool things to get kids interested in mycology, along with reconstituting jelly fungi and locking children in dark closets with bioluminescent mushrooms. H. nidulans is also much sought after as a natural dyeing agent that—again with the help of ammonia—produces purples that are both more vivid and more fast than those produced by other fungi.

A drop of KOH or ammonia on Hapalopilus turns it a crazy purple/fuchsia
—though not as crazy as these web colours are making it look.

Toxicity

And apparently there's also nothing boring about eating this humble little character, though, from the sound of it, there's nothing pleasant about it either. The few cases of poisonings on record, including one adult and two children in the late Eighties, and a father and daughter a couple of years ago, (the latter incident involving the consumption of H. nidulans after misidentifying it as the "beefsteak fungus," Fistulina hepatica), have all been similar in their descriptions of signs and symptoms that happen after a delay of at least 12 hours, the results of dysregulation of central nervous system functions and liver and kidney dysfunction:

• abdominal pain
• nausea and vomiting
• headache
• visual disturbances, including double vision, blurred vision, hallucinations
• multidirectional involuntary eye movements
• balance disorders 
• general weakness
• loss of appetite
• signs of liver and kidney failure
• and violet-coloured urine

The culprit is likely polyporic acid, which can make up an astonishing 40% of H. nidulans by weight. In a lab study, rats given straight polyporic acid via probang developed "strongly reduced locomotor activity, depressed visual placing response and impaired wire manoeuvre," as well as hepatorenal failure and low blood potassium and calcium levels, symptoms that closely parallel those of the people who ate the fungus. I am not sure if the urine of these poisoned rats turned purple or not—but I bet a cat's would! 

Hapalopilus nidulans is watery and soft when fresh and often feasted
on by slugs that are, presumably, unaffected by polyporic acid.

As noted above, the father and daughter poisoned by H. nidulans mistook it for Fistulina hepatica, which is a well-known edible. I have to assume they were not experienced foragers since there are very clear differences between Hapalopilus and Fistulina. Unlike the soft, fibrous flesh of H. nidulans, the flesh of F. hepatica is strangey meat-like, streaky whitish and reddish, and "bleeds" a reddish liquid when squeezed. The surface texture of both cap and stem is finely, and peculiarly pebbly. The tubes on the undersurface are also completely different—easily separable because they are not fused together as they are in most polypores (see my Cyphelloid Wannabes post for more info). 

Two people poisoned by Hapalopilus nidulans mistook it
for an edible Fistulina hepatica, like this one.

Fistulina hepatica has separate, unfused tubes and the
flesh is much more meat-like than Hapalopilus nidulans.

References & Resources:

Michael W. Beug, Polyporic Acid in Fungi: A Brief Note, McIlvainea, Vol. 21

Kraft, J., S. Bauer, G. Keihoff, J. Mieersch, D. Wend, D Riemann, R. Hirschelmann, H-J Holzhausen, J. Langer. 1998. Biological effects of the dihydroorotate dehydrogenase inhibitor polyporic acid, a toxic constituent of the mushroom, Hapalopilus rutilans, in rats and humans. Arch Toxicol 72:711-721.

Villa AF, Saviuc P, Langrand J, Favre G, Chataignerl D, Garnier R: Tender Nesting Polypore (Hapalopilus rutilans) poisoning: report of two cases. Clin Toxicol (Phila); 2013 Sep-Oct;51(8):798-800

Dyeing with Hapalopilus: http://www.allfiberarts.com/library/mushrooms/hap-rutilans.htm

The only other known cause of purple urine

Species descriptions of Hapalopilus nidulans: 

Mycoquebec (as Hapalopilus rutilans)

Mushroom Expert