Excerpts from Jim Conrad's
Naturalist Newsletter

from the September 28, 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

Right beside a house I was painting, where two large roots converged at the base of a trunk of a thriving Texas Live Oak, Quercus fusiformis, there was a fungus the size of a dinner plate I'd never seen before. It's shown below:

Bleeding Oak Fungus, cf. STEREUM, habitat

This is not a typical mushroom with a stem, or even a shelf-type fungus sticking from the trunk like a horizontal ear, but rather it's formed as a crust, with the fungus's bottom attached to its substrate. Most of it is attached to the trunk but notice just to the right of the trunk, at the picture's very top, there's a whitish colony on organic-matter-rich soil. In fact, smaller populations occurred all around the trunk, sometimes on wood, sometimes on the ground, sometimes looking as it little groupings had been splattered there messily. Up close the large body shows more peculiarities, as shown below:

Bleeding Oak Fungus, cf. STEREUM

It's a crust with a mostly gray surface but white along the edges where new growth extends its size, and white in the center area where cauliflower-like growths arise. And on some of the white central cauliflowers there are amber-colored drops of liquid, shown closer up below:

Bleeding Oak Fungus, cf. STEREUM, exuded sap, or

Assuming that these might be dewdrops or drops of sap from the tree, I almost didn't photograph them, but then I remembered that here we seldom get dew and drops of sap weren't visible elsewhere, so I took the picture, and I'm glad, since now I know that they constitute an important field mark. In the centers of the bases of many of the droplets in that picture you can see pinprick-like holes. I'm guessing that they're wormholes from which juices inside the fungus have exuded. The next day, the sap had turned almost black.

One last picture showing the white fungus border extending up a limestone rock on the ground is shown below:

Bleeding Oak Fungus, cf. STEREUM, fungus body creeping up rock

Having never encountered a crust fungus like this I hardly knew where to begin the identification process. I settled on the not-so-technical approach of doing a Google image-search on the keywords "fungus crust oak." Almost instantly a thumbnail popped up showing something similar to our find under the heading "Bleeding Oak Crust Fungus."

Before long I'd learned that in Europe the Bleeding Oak Crust Fungus is fairly commonly documented, and considered to be a member of the genus Stereum. However, in North America, Bleeding Oak Crust Fungi are poorly documented. The Stereum species most closely resembling our live-oak tree seems to be Stereum gausapatum. One fact supporting that observation is that the genus Stereum is said to consist of two groups of species, the "bleeders" and the "non-bleeders," and Stereum gausapatum is a bleeder, like ours with its amber-colored juices issuing from little holes.

Thinking this might be Stereum gausapatum, at MushroomExpert.Com I read Michael Kuo writing that " ... Stereum hirsutum, Stereum complicatum, and Stereum gausapatum, at a minimum, might best be seen as positions along a continuum, and would-be Stereum identifiers should probably be prepared for collections that don't quite settle themselves neatly into one or another position."

Add to this the fact that many experts now accept that the nice genus Stereum needs to be divided into several hard-to-remember genera, and you have a confusing situation. One of those genera is Chondrostereum, which can produce forms looking like ours. So, this is one of a few very rare instances when it seems to me more reasonable to use the rather vague English name "Bleeding Oak Crust Fungus" than a technical binomial about which even the experts are unusually circumspect.

My guess is that eventually the world will decide that it's useless to try to assign classic binomials to certain groups of organisms, such as this one. Also, this group of fungi seems to be so little studied in the Americas there's a very good chance that our Texas Live Oak's population simply doesn't have a generally accepted scientific name we can apply to it.

Stereum species normally take their nutrients from decaying organic matter -- they're saprobic -- so maybe where our fungi climb onto the living tree they're actually drawing nutrients from decaying bark, or a gob of rotting leaves the wind blew into the crack, and so are not parasitic.