#170: Hapalopilus nidulans

Hapalopilus nidulans is small, drab, polypore that most people overlook. However, this humble mushroom is remarkable for two reasons: it is poisonous and it produces a lovely purple dye. It is an uncommon mushroom, which reduces the likelihood of someone eating it but also means people working with mushroom dyes never have enough of it. This mushroom appears on decomposing wood in North America and Europe.

Description

H. nidulans is a bracket or shelf fungus, meaning it grows directly out of its substrate with no stipe. This means the mushrooms are generally semicircular to kidney-shaped, depending on the shape of the surface upon which they are growing.¹ The mushroom grows up to 12cm across and 4cm thick, making it a small to medium-sized mushroom. On top, it features an orangish to light brown or cinnamon surface that is covered in small hairs at first but becomes smooth with time.^1–3 Underneath, H. nidulans produces small pores with flattened edges (“angular pores”) that are colored like the pileus.^1,2

The interior of H. nidulans is colored like the exterior but is often paler, especially near the outside. It has a fleshy texture, which quickly distinguishes H. nidulans from many similar mushrooms that have a tough to woody texture. The most distinctive characteristic of H. nidulans is that it instantly changes color to bright purple when KOH (or ammonia) is applied to any part.^1–3 In Europe, this chemical reaction may result in a dark red rather than a purple.⁴

Ecology

H. nidulans is a white rotter that decomposes “coarse woody debris” (logs and sticks). This mushroom usually grows on the wood of hardwoods, but sometimes appears on conifer wood.¹ You can find H. nidulans in North America and Europe from spring through fall and sometimes during winter in warmer regions. Unfortunately, the mushroom is not common in any part of its range.^1,2 Within North America, H. nidulans is most common east of the Rocky Mountains but it occasionally appears in the Pacific Northwest and the Southwest. In southwestern North America, the mushroom is usually found on conifer debris, which differs from its normal habitat in the rest of the world.¹

Toxicity

Most people consider polypores a basically harmless group. However, there are many exceptions to that generalization (and you should certainly never eat anything you have not identified to species, even if it is a polypore). One of the most significant exceptions is H. nidulans, which contains the toxin polyporic acid.⁴ Polyporic acid (IUPAC name: 2,5-dihydroxy-3,6-diphenylcyclohexa-2,5-diene-1,4-dione) is a small molecule composed of three carbon rings.⁵ This molecule is probably responsible for the color change in H. nidulans.⁴

Symptoms of H. nidulans poisoning include: gastrointestinal distress, blurry vision, inability to balance, loss of kidney function, and purple urine. These symptoms can persist for a few days, but usually clear up within a week.⁶ Studies in mice show that polyporic acid is capable of causing damage to the stomach and kidneys as well as upsetting the balance of chemicals in the blood. Polyporic acid seems to cause these effects by inhibiting the action of dihydroorotate dehydrogenase, which is important in RNA synthesis.⁴

There are other polypores that contain polyporic acid, but H. nidulans is the most dangerous. Polyporic acid can account for as much as 40% of the mushroom’s dry weight. Consequently, even the small fruiting bodies of H. nidulans can be dangerous.⁴

There are many small, brownish polypores that you could confuse with H. nidulans, but most of these are not worth eating. Some of the cases of H. nidulans poisoning happened because someone mistook H. nidulans for the Beefsteak Fungus (Fistulina hepatica, FFF#165).⁶ These two mushrooms are theoretically easy to tell apart based on their descriptions. Pay special attention to the pore surface, which has small angular pores in H. nidulans but in F. hepatica is bumpy or composed of individual pore tubes.

Use in Dyeing

The distinguishing feature of H. nidulans is that it turns purple when a basic solution is applied. People working with dyes extracted from mushrooms found that the purple color works very well as a dye for wool.⁴ 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.⁷ See FFF#159 for more on dyeing with mushrooms.

Taxonomy

H. nidulans is related to the core section of polypores, the Polyporales. Some older texts may refer to it as Polyporus nidulans. A more commonly encountered synonym for this mushroom is H. rutilans.¹ The mushroom sometimes goes by the common name of the “Tender Nesting Polypore,” which is just a translation of Hapalopilus (“soft/tender pileus”) nidulans (“nesting”).³

Kingdom	Fungi
Phylum	Basidiomycota
Subphylum	Agaricomycotina
Class	Agaricomycetes
Order	Polyporales
Family	Polyporaceae
Genus	Hapalopilus
Species	Hapalopilus nidulans (Fr.) P. Karst.8