A Fungus Mystery Unraveled…Kind of

I found some interesting fungi in my back yard a couple months ago. They were growing on the branch of an alder that came down in a storm last year. I took some photos and was eager to do a quick on-line ID, find some intriguing information, put a post together and move on.

My inquiry did not go as expected. But before I get to that, I want to say that I am in no way an expert on fungi. In fact, it might even be pushing it to call myself an amateur enthusiast. But when I do find something I have never come across before I want to know what to call it and find out its story.

At first glance these organisms appeared to be polypores, which are basically fungi that form shelves (conks) on the side of dead or living wood (see red-belted polypore). Unlike many of the mushrooms we come across, the underside of polypores (bracket fungi) contain pores, not gills. Although my sample exhibited shelving with concentric rings similar to bracket fungi, they did not have pores–nor did they have gills. The areas of my fungal samples that were not shelving contained minute folds.

Then I wondered if they could be a type of slime mold (see dog vomit slime mold). They did appear to have some similarities in the way they spread out on the branch, but I was unaware of any slime molds that exhibited shelving.

I ruled out lichens almost immediately, even though many lichens grow as a crust similar to the samples I found (see lichen). The basis for my elimination was color. All lichens have a fungal component. In general, fungi absorb nutrients from dead and decaying plants and are unable to photosynthesise. In the case of lichens the fungus relies on an algae (or cyanobacteria) to provide the photosysthesis as the two species combine to form a single entity. Since photosysthesis is taking place, chlorophyll must be present. Chlorophyll is green, and there was no hint of green in the organism I was trying to identify. They were pure white.

Then I remembered a type of fungus that I had only learned about a month ago, the crust and parchment fungi. Over 400 species of crust and parchment fungi have been recorded in the Pacific Northwest where I live, and more than 1,000 varieties in North America. This group of fungi are corticoid, which means the fruiting bodies grow in a thin layer on the surface of dead wood as a crust, but they can also project out to form shelf-like caps. Now it sounds like I am finally on to something!

Corticoid species are common, but can be difficult to recognize and identify. There is no telling how often I have past by crust and parchment fungi mistaking them for something else.

Of all the crust and parchment fungi I have looked into, the one that seems to be the closest to what is growing in my back yard is Byssomerulius corium (formerly Meruliopsis corium). The exposed surface of this species is described as merulioid, meaning gathered into folds or wrinkles. The common name for this species is netted crust.

Netted crust is weakly zoned, making the color variations of the concentric rings on the caps very slight. The outer edges of the caps are often hairy, yet at times this may be difficult to see without magnification. And most often the netted crust  grows on downed branches rather than the trunk of a dead tree. As the fungi mature they darken and shift to a more brownish color.

All of this description matches perfectly with what I am seeing in my back yard, however I still have doubts as to whether or not I have gotten this one completely right. The caps on the photographs I have seen listed as Byssomerulius corium or Meruliopsis corium vary substantially in appearance. Yet none of the other caps are quite as prominent as the ones I have found. So I guess I am calling this one “probably Byssomerulius corium”.

I know I could have saved you a lot of reading by just getting to the point a little faster, but I wanted to show the mental process that is often necessary when attempting to discover a little something about the mysteries of the natural world.