Deep in the forest, billions of square feet of fungal mycelia permeate through the dense organic layer that is the forest floor. Interactions between species go largely unnoticed underground, as we ourselves cannot see them, and we simply don’t interact with them much. Though, mycophiles like you and I do sometimes catch a glimpse of these intricate interactions when we locate aboveground structures on our fungal forays. The fungus featured in today’s edition of Fungi Friday has quite an interesting ecology, and has perplexed the minds of mycologists for more than a century. Entoloma abortivum parasitizes a few different Armillaria species, but for more than 100 years, it was thought that these Armillaria species are the ones parasitizing. A 2001 study showed the true nature of this fascinating fungal interaction by looking at the ‘aborted’ tissue that emerge from the forest floor.
In late summer through fall, wherever you can locate certain Armillaria species, (like A. tabescens and A. gallica) there’s a good chance that Entoloma abortivum is nearby. Entoloma abortivum is a medium sized, grey mushroom with light pink gills. When the niches of Armillaria and Entoloma abortivum overlap, you are likely to find odd looking, white and puffy ‘aborted’ or carpophoroid forms in very close proximity. These structures vary in size and shape, and actually are comprised of more than on species tissue. In 1974, a Scottish mycologist named Roy Watling, looked at one of these ‘aborted’ forms under the scope and identified the hyphae of two separate species.
Watling proposed that Armillaria grow towards E. abortivum and that the ‘aborted’ form is actually immature, infected fruit bodies of E. abortivum. Although this isn’t correct, this turned heads in the mycological community. For years his theory stood and Armillaria was thought to be the fungal parasite. Armillaria already parasitizes the roots of various tree species, so Watling and others thought that ithad the ability to parasitize fungi as well. This was not the case however. A 2001 study by Daniel Czederpiltz, Thomas Volk, and Harold Burdsall showed otherwise.
Instead of just looking at these carpophoroid structures closely under the scope, these researchers grew Armillaria mushrooms, but inoculated them with mycelia of Entoloma abortivum. Like their field observations, premature fruiting bodies of A. tabescens inoculated with E. abortivum became ensheathed in a mycelial blanket by the true fungal parasite. This experiment quite clearly shows that E. abortivum infects Armillaria species, and reduces the impact of ecologically important tree parasite.
The word parasite has a negative connotation, but sometimes we fail to see that the more parasitic diversity an ecosystem has, the more overall diversity the ecosystem has. Parasites level the playing field, allowing less dominant species to gain an ecological foothold. Armillaria species, are extremely successful tree parasites that grow all over the world. Species like Entoloma abortivum reduce the Armillaria population by dismantling their fruiting body development. The aborted Entoloma is a parasite of a parasite that promotes species diversity in ecosystems all over the world.