I like distinctive, easy to identify fungi. One of these is the Cinnamon Bracket, Hapalopilus nidulans. 

(Cinnamon Bracket is also known by its synonym, Hapalopilus rutilans, but I am using Hapalopilus nidulans because it is the name currently being used by the British Mycological Society.)

Cinnamon Bracket, Hapalopilus nidulans, on a decaying Hazel branch.  January 2025.

“An easily overlooked, unexciting fungus”

You might not think Cinnamon Bracket was distinctive, as it isn’t one of our larger, more impressive species of fungi.

Cinnamon Bracket has a small, fan-shaped to semicircular annual fruitbody no more than 2 – 12 cm (0.8 – 4.7 inches) in diameter, which attaches without a stalk to its substrate, a small log or stick.

Hapalopilus nidulans has an ochraceous to cinnamon brown top that becomes pinkish brown with age, while on the underside the thin-walled angular pores (2 – 4 per millimetre) are the same colour as the top.

To some Cinnamon Bracket is “an easily overlooked, unexciting fungus” but to those of us who appreciate nature’s subtleties it “stops you in your tracks during a woodland walk. Its warm, cinnamon-brown colour and soft, velvety texture make it stand out against the dull greys and greens of decaying wood“.

There is usually a distinct sterile margin around the pores, as in the photograph below.

The underside of a Cinnamon Bracket, Hapalopilus nidulans, showing the pores and sterile margin. October 2022.

Cinnamon Bracket causes a white rot, breaking down lignin, cellulose and hemicellulose. In Europe it usually grows on hardwood species. In Northern Europe the main hosts are Hazel (Corylus avellana) and Sorbus (such as Rowan, Sorbus aucuparia), while in Central europe oaks (Quercus) are the commonest host trees. Hazel is the commonest host in the British Isles.

Hapalopilus nidulans is widespread in Europe as far north as Norway and also occurs in North Africa, Asia, North America and on mountains in tropical Africa (note 1). It has also been recorded from Australia and Oceania. Unusually, it is usually found on conifer debris in south-western parts of North America.

Underside of Cinnamon Bracket, Hapalopilus nidulans, showing pores. this specimen only has a small sterile margin.

I’ve seen Hapalopilus nidulans twice. There are 61 Norfolk record of Hapalopilus nidulans up to the end of 2024, from August to February, and most of these have been on Sorbus, Corylus, Quercus and Betula (birches). At the time of writing, there are 599 records on the NBN Atlas, mainly in England the northern half of Scotland.

Just add KOH

So far, fairly unexciting. But what makes Hapalopilus nidulans really distinctive is the chemical reaction when a drop of an alkaline solution, such as ammonia or potassium hydroxide (KOH), is added to its surface.

Where the alkali meets the fruitbody there is an instant colour change from pinkish brown to vibrant purple. Cinnamon Bracket is transformed from a small, subtle fungus into something truly memorable.

Jan Thornhill’s Weird and Wonderful Wild Mushrooms blog captures the excitement of the colour change: “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” (note 2).

The underside of a Cinnamon Bracket, Hapalopilus nidulans, goes purple when treated with potassium hydroxide solution.

Polyporic Acid

Hapalopilus nidulans contains large quantities of polyporic acid (from 20 to 40% by weight) and it is this which reacts with an alkali to give the purple colour (note 3). 

Most polypore mushrooms are non-toxic and some (such as Chicken of the Woods) are edible and delicious but please don’t eat Cinnamon Bracket, as polyporic acid is toxic to mammals, including humans.

Polyporic acid (2,5-dihydroxy-3,6-diphenylcyclohexa-2,5-diene-1,4-dione) messes up RNA synthesis, specifically the manufacture of uracil, one of the nucleotide bases that form RNA. It does this by inhibiting the enzyme dihydroorotate dehydrogenase, which catalyses the synthesis of orotic acid, which is used to make uracil.

Polyporic acid damages the nervous system, liver and kidneys and eating a Cinnamon Bracket will lead to gastrointestinal distress, blurry vision, inability to balance, loss of kidney function, and purple urine. (The latter would be an impressive party trick but please don’t try this at home!)

The symptoms of poisoning begin about twelve hours after ingestion and can persist for a few days, but usually clear up within a week (note 4).

Polyporic acid also has anti-fungal and anti-bacterial properties and is found in several other species of fungi. Some of these are only distant relatives and the ability to produce polyporic acid is thought to have arisen independently three or four times.

Purple Dye

A safer and more practical use of Cinnamon Bracket is as a source of a lovely purple dye.

Thomas Roehl says (on the Fungus Fact Friday website) that Hapalopilus nidulans works very well as a dye for wool:

“To use this mushroom for dyeing, break it up into small pieces and place it in hot water with pre-mordanted wool. Then use ammonia to adjust the pH up to 9. The ammonia turns the mushroom purple. That color leaves the mushroom and adheres to the wool, turning it anywhere from a deep purple to a bright lavender. You normally use a 1:1 dry weight ratio of mushroom to wool, but H. nidulans is a strong dyer and you can probably use less. This is good, since H. nidulans is a fairly uncommon mushroom.”

Ann on the Shroomworks website (“Hapalopilus, Ever Abundant“, June 2018) gives more practical advice for dyeing with Hapalopilus nidulans and shares the results, some beautifully coloured balls of wool. She confirms that a small amount of the fungus goes a long way and has used a 150 gramme (5.2 oz) sample from Sweden about thirty times.

Jenny Dean also writes about dyeing with Hapalopilus nidulans (“South Downs Yarn & colours from fungi“) and the North American Mycological Association website gives details of this and other fungi that can be used for dyeing (“A Short Selection of the Best Mushrooms for Color“). This article also mentions Inonotus hispidus (Shaggy Bracket), which I wrote about a few months ago, not realising it could be used for dyeing.

I found my second Cinnamon Bracket a month ago in woodland to the west of Norwich while on a bike ride with my wife Vanna. I was pretty sure what it was but hadn’t taken my bottle of KOH out on my bike ride, so I took it home to check (note 5).

I’ve dried the bracket and passed it to my friend Sarah, who dyes fabrics. I hope to see the results soon and, if the dyeing is successful, I’ll share the results.

Other Names for Cinnamon Bracket

In Welsh, Cinnamon Bracket is Ysgwydd Sinamwn. Other English names for Hapalopilus nidulans (used in the United States) include Purple Dye Polypore and Tender Nesting Polypore. The specific name nidulans means “nesting”; rutilans is “orange-red” in Latin. Hapalopilus is from Ancient Greek, meaning “tender cap”.

Possible Confusion: Beefsteak Fungus

I think Cinnamon Bracket is pretty distinctive, even without the help of KOH, but a novice might possibly think that Hapalopilus nidulans was a very small Beefsteak Fungus (Fistulina hepatica) and indeed a 2013 poisoning by Hapalopilus nidulans occurred when someone mistook a Cinnamon Bracket for a Beefsteak Fungus.

Unlike a Beefsteak Fungus, Cinnamon Bracket never “bleeds” or reaches the size of a mature Beefsteak. The pores of Fistulina hepatica are straw-yellow, becoming reddish-brown as the fruiting body ages and unlike Hapalopilus rutilans they bruise deep red-brown. Fistulina hepatica is mainly found on oaks and Sweet Chestnut (Castanea sativa) in late summer and autumn, from August to October.

Beefsteak Fungus, Fistulina hepatica. This one is “bleeding” slightly.

Unlike Cinnamon Bracket, the Beefsteak Fungus is edible, though mainly for the novelty of eating a fungus that looks like raw meat or liver. It can be consumed raw or cooked. I cooked it once and found it pleasant enough and would eat it again, though it was a bit acidic and lacked the balance of flavours that makes Chicken of the Woods so enjoyable. I agree with the First Nature website: “as an edible species it does not really live up to its good looks” (note 6).

Beefsteak Fungus, Fistulina hepatica. “Edible, though mainly for the novelty of eating a fungus that looks like raw meat or liver”.

In contrast to a Beefsteak Fungus: The top surface of Cinnamon Bracket, Hapalopilus nidulans.

Notes

Note 1 – In “Poroid Fungi of Europe” Ryvarden and Melo use the name Hapalopilus rutilans.

They list its hardwood hosts as Acer, Aesculus, Alnus, Betula, Carpinus, Corylus, Crataegus, Fagus, Ficus, Fraxinus, Malus, Pittosporum, Populus, Prunus, Quercus, Robinia, Sambucus, Salix, Sorbus and Tilia. It occasionally grows on conifers such as Abies, Picea and Pinus. Pages 182 – 183, L. Ryvarden & I. Melo (2022). ‘Poroid Fungi of Europe’. 3rd edition. Fungiflora, Oslo, Norway.

Note 2 – In “Poroid Fungi of Europe” Ryvarden and Melo give the colour with KOH as “a vivid violet”. This is what I’ve found when I’ve treated specimens with KOH, as shown in my photograph above.

However, Michael W. Beug (in “Polyporic Acid in Fungi: A Brief Note“) says that “Ko, Jung and Ryvarden (2001) give the reaction between Hapalopilus nidulans and KOH as strongly cherry red, though North American collections give a lilac to violet reaction”. (See Ko, K.S., H.S. Jung and Lief Ryvarden (2001). “Phylogenetic relationships of Hapalopilus and related genera inferred from mitochondrial and small subunit ribosomal DNA sequences.” Mycologia Vol 93(2): pp 270 – 276.)

Note 3 – Michael W. Beug (in “Polyporic Acid in Fungi: A Brief Note“) speculates that the colour change “is the result of an acid-base reaction and that any base would produce the color change by removing an acidic proton” and this is the best explanation I have found. Please let me know if you find more details of this chemical reaction.

Not all colour changes with KOH are caused by polyporic acid. For example, the Hoof Fungus (Fomes fomentarius) goes dark blood red when a drop of KOH is added to a piece of tissue from the upper surface but this is due to the presence of fomentariol, a benzotropolone. (Arpin, N., J. Favre-Bonvin, W. Steglich  (1974): “Fomentarol: A New Benzo Tropolone Isolated From Fomes fomentarius“. Phytochemistry Vol. 13 (9), pp1949 – 1952).

The paper “Pigments of Higher Fungi: A Review” is worth a read if you want to know more about the many pigments that occur in the colourful kingdom of fungi.  J. Velisek & K. Cejpek (2011), Czech Journal of Food Sciences Vol. 29(2), pp87 – 102.

Note 4 – On the Weird and Wonderful Mushrooms website Jan Thornhill gives more details of Hapalopilus nidulans poisoning:

“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 Jungle Dragon website mentions two poisoning cases – presumably the same ones – reported in 1992 (a family of three in Germany) and 2013. In both cases the symptoms started about 12 hours after ingestion and consisted of nausea, impaired movement, visual impairment, liver and kidney failure. The patients’ urine was purple. Everyone involved had recovered fully a week later.

Note 5 – We found a few other fungi here, including Spring Hazelcup (Encoelia furfuracea), Alder Scalycap (Pholiota alnicola) and Blushing Bracket (Daedaleopsis confragosa).

I would ideally have tested the bracket with KOH in the field, leaving it as a habitat for small invertebrates such as beetles.

Note 6 – Most wild fungi should be cooked before eating. Beefsteak Fungus is one of the few that is safe to eat when raw. Chicken of the Woods, in contrast, must be cooked and you should it eat with caution the first time you try it, as it can cause gastric upsets in some people.