Desarmillaria caespitosa

January 10, 2022

Good evening, friends,

This week’s mushroom is Desarmillaria caespitosa, commonly known as the ringless honey mushroom. This mushroom was found by Jerry in the ramble on 8/31/2021.

Up until 2021, this fungus was known as Desarmillaria tabescens, and prior to that, it was Armillaria tabescens. D. caespitosa was involved in a “taxon split” and is now recognized as the North American vicariant (relative) of D. tabescens – which is found in Europe and Asia. Due to this taxon split occurring last year, a lot of the information I’m sourcing from is referring to D. tabescens, but all the general information I include should be the same across the two species.

You may also have noticed D. caespitosa used to be in the same genus as last week’s Armillaria mellea, and they’re closely related, but this mushroom is easier to ID for one major reason alluded to in the common name.

Fun Facts

Last week we highlighted rhizomorphs, the black mycelial cords that are very characteristic of Armillaria species. However, according to Michael Kuo (reference 1), D. caespitosa doesn’t create these mycelial cords. Since the fungus doesn’t use mycelial cords, it relies on infected roots coming into contact with other suitable hosts to help it move through the soil.

There is research that shows that D. tabescens produces a chemical compound that has anti-cancer properties. A study examining an extract of the mushroom in vitro (outside of a living organism) showed it contained compounds effective against different types of bacteria that are known to be harmful to humans. I imagine a lot of the chemical compounds are the same in the European and North American species, so this is yet another mushroom with promising medicinal properties.

Similar to last week, D. caespitosa also has bioluminescent mycelium. If you’re still curious about this phenomenon then you’ll quite enjoy next week’s mushroom 😉

Ecology

In the first photo, it looks like the mushrooms are popping out of the dead log lying on the ground. However, if you look at the photo above it reveals that this is not the case. Further examination would reveal these mushrooms are in fact growing out of a tree root – dead or alive. Similar to last week’s A. mellea, this fungus is both parasitic and saprobic. The major difference between the two species, and the key identifying feature, is that D. caespitosa doesn’t have a ring (annulus) on its stipe like our honey mushroom from last week. This is evident in the photo below. D. caespitosa grows late summer through fall in North America, and the species it was formerly lumped in with, D. tabescens, grows in Europe and Asia during the same seasons.

The picture below shows what appears to be white powder on the caps of these mushrooms. These are actually spores that have been released from the gills of the mushrooms growing above them. As you can see, the tallest mushroom in the picture below doesn’t have any white spores on its cap whereas nearly all the mushrooms below it do. This is an instance where you don’t need to take a specimen home for a spore print since the mushroom’s copious spore production has already given you an in situ spore print. If you’ve read this far I’ll reward you with a mind-blowing fun fact from Peter McCoy’s Radical Mycology: the annual weight of basidiospores (all the spores released from mushrooms in the phylum Basidiomycota – this includes D. caespitosa) is approximately 17 megatons or the weight of 100,000 blue whales. You’re breathing some of them in as you read this.

Wear an extra layer tomorrow,
Aubrey

References
1) Kuo, M. (2017, May). Armillaria tabescens. Retrieved from the MushroomExpert.Com Web site: http://www.mushroomexpert.com/armillaria_tabescens.html
2) Antonín V, Stewart JE, Ortiz RM, Kim MS, Bonello PE, Tomšovský M, Klopfenstein NB. Desarmillaria caespitosa, a North American vicariant of D. tabescens. Mycologia. 2021 Jul-Aug;113(4):776-790. doi: 10.1080/00275514.2021.1890969. Epub 2021 Apr 29. PMID: 33914673.
https://pubmed.ncbi.nlm.nih.gov/33914673/
3) https://www.first-nature.com/fungi/desarmillaria-tabescens.php
4) https://www.messiah.edu/Oakes/fungi_on_wood/gilled%20fungi/species%20pages/Armillaria%20tabescens.htm
5) https://healing-mushrooms.net/ringless-honey-mushroom#_edn3
6) https://www.inaturalist.org/taxa/1238700-Desarmillaria-caespitosa