Mycobank Taxonomy: Fungi, Dikarya, Basidiomycota, Agaricomycotina, Agaricomycetes, Agaricales, Pluteaceae, Pluteus
Some fungi are "rare" simply because they are obscure and nobody besides myconerds looks for them. P. aurantiorugosis, on the other hand, is a gorgeous, photogenic mushroom. Despite the fact it stands out, it is seldom documented, and thus can be regarded as truly rare. For example, Michael Kuo from mushroomexpert.com has only found it once in 20 years of mushroom hunting.
I am continuously surprised by the forest behind my house. It's a cruddy place - buckthorn, honeysuckle, and box elder run the woods; trash is scattered about or heaped into dumpy piles; and invasive fungal pathogens are devastating the hardwood trees. Yet, it is full of treasures. In addition to the truffle I recently found, it is also where I discovered this mushroom. The scarlet-red fruiting bodies were growing off the end of a fallen, decorticated trunk. I puzzled over them for a long time. They were so distinct yet they didn't fit any description in my head. Once I noticed the free, pinkish gills, I knew it was a Pluteus species and identification was only a quick Google search away. To my surprise, this was the first documented encounter of P. aurantiorugosis in Michigan since the 1970s!
The first fruiting was quite large. I collected a portion of it for preservation in the MICH fungarium and to sequence its DNA. Unexpectedly, a few weeks later it fruited again. That's when I got the idea to try eating it – I might never see this mushroom again! I first conducted an extensive literature search on P. aurantiorugosus, its synonyms, P. leoninus var. coccineus and P. caloceps, and its basionym, Agaricus aurantiorugosus, for any information regarding edibility. This species was first described in 1857 by the Swedish mycologist Jacob Gabriel Trog (1781-1865) in the journal Mittheilungen der Naturforschenden Gesellschaft in Bern. The original description, in German, can be found here:
Der 1 1/2 - 2 1/2" lange, 2-4" dicke. Strunk ist unten etwas verdickt, wird aber nach oben allmälig dünner, blassgelb, an der Basis röthlich, inwendig dicht, blass, mit braunen Längsfasern durchzogen. Der anfangs glockenförmig, bucklig, dünnfleischig; das Fleisch von weisslicher Farbe; die Oberfläche des Hutes ist uneben, netsförmig-runzlig, von einer gelbrothen Farbe, welche im mittlern Theil des Hutes fast in's Zinnoberrothe übergeht. Die sehr gedruangten Lamellen sind anfangs weiss, dann fleischröthlich, sägeförmig gezähnt, 2" breit und gänzlich frei. Die röthlichen Sporen sind rundlich. Er ist geruchlos.
In other words:
1 1/2 - 2 1/2" long, 2-4" thick. Stipe is somewhat thickened below, but becomes gradually thinner upward, pale yellow, at the base reddish, internally dense, pale, with brown longitudinal fibers traversed. Bell-shaped at first, hunchbacked, thin-fleshed; the meat of whitish color; the surface of the cap is uneven, "netsförmig"-wrinkled, of a yellow-red color, which in the middle part of the cap almost turns into vermilion. The very compacted lamellae are white at first, then flesh-red, serrated, 2" wide and completely free, the reddish spores are roundish, odorless.
A great morphological fit, but nothing on edibility. I wasn't able to access the 1909 journal article by George Francis Atkinson describing the North American species Pluteus caloceps nor was I able to find the article that officially synonymized all these taxa. Else C. Vellinga published a monograph on Pluteus in volume 2 of Flora Agaricina Neerlandica (1990) at which point all these taxa were already considered synonyms of one other. One thing stood out to me in Vellinga's description of P. aurantiorugosus: they report the smell to be absent and the taste to be bitterish. Conversely, these mushrooms had a radishy smell and not much of a taste.
Next, I checked out more modern material to get a sense of the phylogeny of Pluteus and whether P. aurantiorugosus is closely related to more commonly eaten species. P. aurantiorugosus belongs in sect. Celluloderma (Justo et al., 2011), which contains a number of seemingly rare species, including species listed on the IUCN Red List, but all of unknown edibility. No help there.
Finally, I found one published source that mentioned edibility. Boa (2004) lists P. aurantiorugosus as a species consumed for food in Mexico, but cites www.semarnat.gob.mx as the source of this information. Unfortunately, this citation is useless for determining the veracity of their claim. The last source I can mention is an anecdote on the website Abney Fungi in which the author reports, "One man in Abney tried it for possible psychedelic properties because its colour looked as if it might be interesting. It wasn’t. He was unwell for a week after very few sample caps were eaten." Besides being a terrible idea to eat mushrooms because their colors are interesting, blue bruising - not red caps - is suggestive of the presence of psilocybin. Furthermore, P. salicinus is the only member of the genus known to have magic traits. But yes, there is indeed a Pluteus species that is psychedelic and it is found scattered across eastern United States. Moving on...
So, I found two reports mentioning the edibility of P. aurantiorugosus, both secondhand and unverifiable. One report says it is eaten in Mexico, the other that it is poisonous in England. With that, I collected a mushroom for edibility testing as outlined by Dr. Chester Leathers from the Arizona Mushroom Society. I chopped the mushroom into thin sections and fried them in butter. At first, the odor was unpleasant, sour, acidic, like vomit. Then, it mellowed out. Finally, once the water had evaporated and it browned, the mushroom smelled deliciously nutty, like hazelnuts. The first step was taking a small amount (less than a teaspoon), chewing it, spitting it out, and waiting an hour to see if I had an allergic reaction. The taste was very good. No allergic reaction. Next, I ate a teaspoon. In a short bit, I developed mild stomach discomfort that eased over two hours. I am sensitive to the powers of placebo and can't be sure if that experience was a direct result of the mushroom, but given the noticeable change in my stomach, I think it would have been foolish to continue with the testing. Maybe it was foolish of me to test this unknown mushroom in the first place.
This was my first experience testing the edibility of a truly unknown mushroom. I felt comfortable doing so given the absence (as far as I am aware) of poisonous substances in the family Pluteaceae, which was affirmed by Danny Miller, Education Chair for the Puget Sound Mycological Society. Any mentions of poisonous Pluteaceae species seem to be directed at the aforementioned psychedelic P. salicinus, in which case "poisonous" is subjective. From this website, I also learned that a radish-like smell is characteristic of species in sect. Pluteus, not sect. Celluloderma, which are supposed to be odorless. I observed a radishy smell in this specimen, which makes me extra curious to sequence its DNA to solidify my identification.
Anyway, this experience affirmed a few important things for me. For one, just because there are edible species in a genus does not mean that other members of that genus are edible. Amanita, Agaricus, Cortinarius, Entoloma, and probably most other genera with some edible species also contain species that are poisonous, even deadly. It's something obvious that nevertheless must be restated and reminded again and again. Why else would mykoweb.com list P. romellii, sister species to P. aurantiorugosus, as "probably edible" if not for the unsubstantiated belief that edibility can be inferred across a genus? Ignorance is not evidence to reject the null hypothesis of not edible. While the consequences of recklessly testing this belief might be less severe for genera that are not known to contain deadly mycotoxins, it might still lead to bad outcomes. Be cautious!
"Yeah, Alden, be cautious!"
ACD0168, iNaturalist #32772099; 14 September 2019; Washtenaw Co., MI, USA; leg. Alden C. Dirks, det. Alden C. Dirks; GenBank #MZ919169 (ITS rDNA), MICH 352174.
Boa, E. (2004). Wild Edible Fungi: A Global Overview of their Use and Importance to People. Food and Agriculture Organization of the United Nations.
Justo, A., Minnis, A. M., Ghignone, S., Menolli, N., Capelari, M., Rodríguez, O., … Vizzini, A. (2011). Species recognition in Pluteus and Volvopluteus (Pluteaceae, Agaricales): Morphology, geography and phylogeny. Mycological Progress, 10(4), 453–479. https://doi.org/10.1007/s11557-010-0716-z
Trog. (1857) Mitt. naturf. Ges. Bern, 388, 32.
Vellinga, E. C. (1990). Pluteus. In: Bas, C., Kuyper, T. W., Noordeloos, M. E., Vellinga, E. C. (eds.). Flora Agaricina Neerlandica Volume 2. A. A. Balkema, Rotterdam, 31–55.
The material on aldendirks.com is presented for general informational and educational purposes only, and under no circumstances is to be considered a substitute for identification of an actual biological specimen by a person qualified to make that judgment. Some fungi are poisonous; please be cautious. All images on this website are licensed under Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0).