Species Feature #9, Ash-Tree Bolete

This feature is long overdue. In many ways the ash-tree bolete (Gyrodon merulioides) should have been Species Feature #1. Without this mushroom, my blog wouldn't exist. It was my first mycology success story: I encountered several specimens growing just outside my apartment. I had no idea what they were, but was able to get a tentative ID from one source. Since I was inexperienced, I really wanted corroboration - so I Googled the scientific name. At the time, one of the first search results took me to a post in this livejournal. It's written by a zoo employee in New England, and it planted the seed that grew into my idea for this blog. My introduction to this DC area blog by Laurel was, I suppose, the fertilizer. But it was my interest in G. merulioides that served as the soil. My blog's synthesis bears remarkable parallels to the ecological niche occupied by this species.

One largish specimen

Gyrodon merulioides Quick Facts

Common Name(s): ash-tree bolete

Taxonomic Breakdown:

• Kingdom - Fungi
• Subkingdom - Dikarya
• Phylum - Basidiomycota
• Subphylum - Agaricomycotina
• Class - Agaricomycetes
• Order - Boletales
• Family -Paxillaceae
• Genus - Gyrodon
• Species - merulioides

Range: I couldn't find information directly on the range of this species, but it is limited to the range of ash trees. Most commonly it is found under white ash, Fraxinus americana.

Just a small sampling of the hundreds of specimens I found one day in Silver Spring

Because of its proximity to white ash, the ash-tree bolete was long thought to be mycorrhizal.This is generally the case when a mushroom species is found exclusively under one species (or in this case, one related group of species) of tree. Yet the life of G. merulioides is more complex than that. It instead participates in a totally different symbiotic relationship - with a species of aphid which itself only feeds on ash trees. Meliarhizophagus fraxinifolii, according to this press release, fights predation by breeding wildly... so wildly, in fact, that some generations are born pregnant. I won't pretend to understand how this happens, but it adds one more layer of fascination to the scene.

Unfortunately, in the 1990s a fourth species entered the picture: the emerald ash borer (Agrilus planipennis), often referred to as simply EAB. This species of beetle decimates populations of ash trees, and threatens the entire genus. I have previously written about invasive species, taking the position that we are often too quick to label introduced species as damaging to their new environments. However, this seems like a clear-cut and very serious problem. Forests in this area can ill afford the loss of yet more tree species, and the EAB threatens several, and no North American species of ash tree has yet shown effective resistance to infestation. Lose the trees, and this biome loses the aphid and the mushroom mentioned above. Lose the aphid, and its predators lose a food source which rapidly replenishes itself.

Collecting spores.

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This mushroom is easy to identify if one knows what to look for. From above, the irregular, leathery, brown caps can be easy to miss, but once seen these alone are a good indicator of what you're looking at. The stem is lateral and often not very substantial. Underneath, the pore surface is a solid yellow with hexagonal pores. The light yellow (sometimes white) flesh of this bolete, like that of many boletes, bruises blue. A spore print usually isn't necessary for identification, but if taken it will appear olive brown. If you're unsure, look around for ash trees.

Note the blue bruising, and how the pores peel away from the flesh as a discreet layer.