Excerpts from Jim Conrad's
Naturalist Newsletter

Rusty-gilled Polypore, GLOEOPHYLLUM SEPIARIUM, on dry wood

from the February 23, 2014 Newsletter issued from the Frio Canyon Nature Education Center in the valley of the Dry Frio River in northern Uvalde County, southwestern Texas, on the southern border of the Edwards Plateau, USA
RUSTY-GILLED POLYPORE

Way up the canyon along the road years ago someone left on the ground what at one time must have been a pretty good four-by-six board. Now it was weathered and decaying. When I turned it over to see if anyone interesting sheltered below it, I found sticking to the board's underside what's shown above.

We've all seen shelf or bracket fungi, those sometimes big and sometimes tough mushrooms emerging from the sides of sick or dead trees or logs like huge ears. Normally such fungi are attached by their sides, with a distinct cap above and spore-producing gills or pores below. What's in the picture appears to be nothing but gills, with the cap completely absent. Beneath the board the gills had been pointing downward, as they should to release spores.

Seeing that a fungus could configure itself so strangely was just the beginning of my introduction to a spectacularly nonconformist species. Its features were so inconsistent with my preconceptions about how a fungus should behave that I ended up having to identify it not by its technical features, but by browsing the Internet looking for labeled pictures. And I did find pictures, looking just like ours.

It's the Rusty-gilled Polypore, GLOEOPHYLLUM SEPIARIUM, and if you know the basics of mushroom classification probably calling this a polypore sounds wrong. Polypores should release their spores from pores on the mushroom's undersurface, not from gills such as those shown by our polypore. All decent mushroom hunters know that you just don't get polypore-type mushrooms with gills.

However, our Rusty-gilled Polypore is a polypore with gills. Gene sequencers have confirmed that the species is a genuine member of the Polypore Order, the Polyporales. Many eons ago, during the course of mushroom evolution, polypores diverged from gilled mushrooms in the order Agaricales, and it's true that the vast majority of polypores do have pores, not gills, but the Rusty-gilled Polypore has gills anyway. A closely related species, Gloeophyllum trabeum, produces a mixture of gills, pores, and maze-like areas.

It's a matter of convergent evolution -- of gills evolving independently in fungi on different branches of the Tree of Life. You can see why gills would be such good adaptations: Because they so dramatically increase a fungus's spore-producing surface area relative to its mass.

Beyond all that, the Rusty-gilled Polypore's job in Nature is to decompose deadwood, especially of conifers such as pines, but sometimes also of hardwoods such as oaks. The board our fungus was attached to looked like pine; notice the black, shiny resin that's oozed from splits and hardened. The Rusty-gilled Polypore often occurs on lumber that's been stored too long, and old house decks constructed of pinewood, where its effects are said to constitute brown rot. Wood with brown rot looks brown, dry, and crumbly.

Rusty-gilled Polypores occur throughout most of North America and Europe, especially in the conifer zones. In the Dry Frio Valley we have no conifers except for a very few Pinyon Pines atop some isolated hills, so it's pretty impressive that our fungus managed to find a pine board in such an out-of-the-way spot.