Tom Volk's Fungus of the Month for July 2003

This month's fungus is Gyroporus cyanescens, the blueing bolete

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"Broken and Blue"
A video starring Gyroporus cyanescens
Introducing Bernadette O'Reilly, in her screen debut as a hand model.

Copyright © 2003 by Tom Volk. Please do not link to this video without permission.
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Gyroporus cyanescens photo by Georg Müller at http://www.pilzepilze.deThis month's fungus is a fun one to find while you're hiking through the woods. It's an innocuous whitish tan mushroom-- until you bruise it or break it, when it turns a vivid blue! This beautiful picture of the Kornblumenröhrling is courtesy of Georg Müller at, a marvelous German mushroom site, started a month before mine in 1995, with hundreds of picture, lots of information, many annotated mushroom links, and even a forum! Georg is a weather forecaster by profession-- doesn't that sound like a great combination with mushrooming!? I would sure like to hear a "mushroom forecast" on my local news!

Gyroporus cyanescens is a delicious edible mushroom. However, this is contrary to the Bolete Rule, which states that "you can safely eat any bolete EXCEPT ones that turn blue when bruised and/or have a red or orange pore surface." Following the Bolete Rule, this mushroom, as well as many other edible boletes, would be excluded. This rule also does not guarantee deliciousness; you may not have a pleasant dining experience with all boletes that fit this rule, because some of them are very bitter or otherwise disagreeable or just bland. However, if you follow the Bolete Rule you are very unlikely to get poisoned. However, a more important rule is to identify your mushrooms to species and consult expert advice before you eat any wild mushroom. There are many new mushrooms waiting to be discovered, and we know nothing about their edibilty or toxicity.

Variegatic acid and its conversion to a  blue compound by oxygen in the presence of oxidaseThe blueing reaction is easily explained through biochemistry. A compound called variegatic acid remains colorless unless it is exposed to oxygen. The cell walls of Gyroporus cyanescens are easily broken, exposing the variegatic acid to the air. The oxygenase enzyme converts the variegatic acid to its quinone methide, which is blue. Interestingly, in many other boletes, in the absence of oxygen, variegatic acid is converted to variegatorubin, which is responsible to the red color found in many members of this group. The possible functions of the variegatic acid and its color shifts to blue or red are unknown. Anyone have any ideas?

I have seen this mushroom mainly east of the Great Plains, from Minnesota to North Carolina to Vermont, but it also occurs in Europe. It seems to prefer the more northerly climate. My friend Theresa Rey of the Asheville Mushroom Club in North Carolina tells the story of seeing something that she thought looked like a great fruiting of Gyroporus cyanescens in the mountains of North Carolina. The only problem was that the group of mushrooms was 20 feet down a steep ravine! It would probably be worth climbing down the ravine to collect these edible mushrooms, but what if they were something else, not as delectable? Theresa, being enterprising, found a solution: throw small rocks at the mushrooms and check with binoculars to see if they bruised blue. In fact they did turn blue, and Theresa and her friends collected them and had a great meal. Remember, however, that the mere blueing of the mushroom does not indicate that you have an edible mushroom-- quite the contrary, since the bolete rule states that beginners should avoid boletes that bruise blue. You must still use all the other characters to correctly identify a mushroom *to species* before you can eat it, as Theresa and her friends did, once they got up close to the mushrooms.

There are a couple of other relatively common species of Gyroporus, including G. purpurinus, the red Gyroporus, and G. castanaeus, the chestnut bolete. Both are named for their color, although I have (coincidentally) found G. castanaeus commonly asssociated with American chestnut here, as well as with oaks. Neither species exhibits any staining reaction where bruised, but both have the characteristic yellow spore prints.
Bolete pores, macroscopically and microscopicallyBoletes have mushroom-like fruiting bodies, but have small pores on the undersurface instead of gills. Like gills, these pores are lined with basidia that produce basidiospores, the sexual spores of the Basidiomycota. In the photos to the left, the top photo shows a close-up of bolete pores. The bottom photo is a section of the pore surface. If you look closely you can see the irregular edge on the inside of the pores; this represents the basidia with the attached basidiospores.

Boletes also have other characteristics that hold the group together. The pores peel away from the cap very easily. Compare this to the polypores, in which the pores are an integral part of the fruiting body and cannot be peeled away. In addition to this, all of the boletes are apparently mycorrhizal, forming a mutualistic relationship with the roots of trees, while almost all polypores are saprobic wood decay fungi.

Like the gilled mushrooms, several genera can be delimited based on the color of the spore print. For example, the genus Boletus (including Boletus edulis, and the genus Leccinum have brown spores (Those two genera are easily separated by the scabers on the stalk of Leccinum species). Tylopilus, including Tylopilus felleus, the bitter look-alike for Boletus edulis has pink spores. Gyroporus species have yellow spores.

Because of their mushroom-like shape, the boletes were once classified with the gilled mushrooms in the Agaricales, but in their own family, the Boletaceae. Most mycologists now consider the boletes to be in a separate order, the Boletales, because of significant differences in the spores and the organization of the tissues in the fruiting body. DNA studies have now confirmed this separation. According to similar DNA systematics studies, the boletes are probably evolutionarily related to the false puffballs, such as Scleroderma and Pisolithus tinctorius

I hope you enjoyed learning something about boletes today, in particular the color changes that occur in many of them upon bruising or breaking. Remember the Bolete Rule, but also remember the limitations of the rule.

If you have anything to add, or if you have corrections, comments, or recommendations for future FotM's (or maybe you'd like to be co-author of a FotM?), please write to me at

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