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Chestnut Bolete - Gyroporus castaneus

Good afternoon, friends, and Happy Valentine's Day.

This week's mushroom is Gyroporus castaneus, commonly known as the chestnut bolete. This mushroom was popping up all over the park this past summer and the pictures feature specimens from the ramble and the north woods. This is the first time we've featured a bolete on MushroomMonday which is quite exciting and we'll discuss what that means below.

Gyroporus castaneus

Fun Facts

G. castaneus possesses polysaccharides (carbohydrates, long chains of sugar molecules) that displayed anti-carcinogenic properties in one study conducted with white mice. The polysaccharides were injected into the mice and reduced the growth of Sarcoma 180 tumors by 80% and Ehrlich solid cancers by 70% (reference 4). It's one study from 1973 but there is promise, potential, and purpose for further research involving this fungus and the whole world of medicinal mushrooms.

Gyroporus castaneus

G. castaneus is edible as well. I remember my former manager Eric telling me that the great Gary Lincoff specifically pointed these out to him when they went on a walk together. Perhaps the most important identifying factor of this mushroom is the hollow/chambered stipe (stem). In young mushrooms there will be white, fibrous, cottony strands occupying space in the stipe (seen best in the picture below) but the stipe hollows out as the mushroom ages. Along with the chestnut/orange color and smaller size, this unique feature will help you identify this bolete when you happen upon it in the park/woods. Some people reported the mushroom giving them gastrointestinal distress so, as with any foraged mushroom, eat a tiny bit at first to make sure it suits you and don't eat something solely because you read about it in an email - seek out multiple sources of information.

Gyroporus castaneus


As you may have noticed, this mushroom has the physical structure of a lot of gilled mushrooms we've looked at, but instead of having gills underneath the cap it has a spongy surface with tiny tubes called pores. This is characteristic of boletes. Spores are released from these pores and this method of spore dispersal is the same as the polypore mushrooms we've previously seen (like chicken of the woods). The color of the spores are light yellow, "straw colored" was a nice description I read, and that turns the white pore surface to an off-white, straw color in mature mushrooms.

Gyroporus castaneus

G. castaneus is mycorrhizal, meaning the fungus forms a relationship with plant roots (specifically oak roots for this species) where nutrients are exchanged in symbiosis. In the above picture the mushrooms are popping up right through oak leaf litter. G. castaneus is found in temperate forests across the Northern hemisphere (eastern North America, Europe, and Asia) but also specimens have been found in Australia and New Zealand. As far as boletes go, this mushroom is on the smaller end with the cap reaching 10 cm across at its largest. In NYC you'll find this diminutive bolete popping up from late June through July.

Gyroporus castaneus

One interesting ecological tidbit I came across while researching this mushroom was from Thomas Roehl - the brain behind another alliterative fungal website He postulates that while G. castaneus is listed and widely accepted as mycorrhizal, he has seen instances where it appears to be saprobic - consuming nutrients from dead organic material. Two reasons for this hypothesis are that he has found the mushrooms growing in wood chips and has found them farther than 10 meters from their suspected oak partners. He suggests the fungus may be "facultatively mycorrhizal" where it can switch between mycorrhizal or saprobic depending on ecological conditions and nutrient availability. Mycorrhizal fungi begin as saprobes before they find a plant partner so this isn't an unprecedented hypothesis and perhaps more research on the species is warranted.

I found this mushroom growing in the severely degraded "sassafras grove" in the ramble (which has some other, less savory, monikers for those in the know - a lot of nighttime activity transpires in between those weary sassafras). I was impressed to find it growing in such a degraded, compacted landscape but I suspect it was growing with the few large oaks on the periphery of the area.

Full moon on Wednesday,


PS. Ethan from the New York Mycological Society contributed an additional fun fact for last week's Daldinia profile. He noted that Daldinia species release their spores nocturnally (originally discovered by mycologist C.T. Ingold). This phenomenon births several questions and perhaps the most pressing would be how does the fungus know it's night? And what is advantageous about releasing spores at night? Maybe some insects that eat Daldinia spores are active at night? An added layer of mystery, a puzzle piece in fungal science, that we are left ponder.


1) Kuo, M. (2013, December). Gyroporus castaneus. Retrieved from the MushroomExpert.Com Web site:


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