Interesting, if it is, it could be a very medicinal mushroom..

"Mesima is a highly respected medicinal mushroom used most commonly in Japan, Korea, and China for centuries to prevent ailments as diverse as gastroenteric dysfunction, diarrhea, hemorrhage, rheumatoid arthritis, allergies, and a variety of cancers. Recently Identified as having the highest anti-tumor activity of the group of mushrooms containing most of the medicinal species"
http://myriadmycology.com/store/index.php/mushrooms/mesima-sang-huang-mushroom-powder-456gram

"Mounting evidence from different research groups has shown that PL induces apoptosis in a host of murine and human carcinomas without causing any measurable toxic effects to their normal counterparts. Recently, research has been focused on the anti-tumor effect of PL, and in particular, on its ability to enhance some conventional chemotherapeutic drugs. These studies suggest PL to be a promising candidate as an alternative anticancer agent or a synergizer for existing antitumor drugs. Hereinafter, we summarize the present progress in elucidating the mechanisms underlying the potency of PL and its anti-tumor function. The fractionation and identification of the biologically active components from PL are also briefly introduced."
http://www.ncbi.nlm.nih.gov/pubmed/18537612

"Health Benefits of Phellinus Linteus
1) Cancer
2) Diabetes
3) Eczema"
http://altmedicine.about.com/od/Medicinal-Mushrooms/fl/Phellinus-Linteus.htm

Here is a link that might be useful: Phellinus Linteus (Mesima, Meshimakobu, Song-Gen, Sang-Hwang)

Ours would likely have different properties from the Asian species?

What about this one - also possibly Phellinus linteus (Black Hoof Medicinal Mushroom)?

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Natural Sang Hwang has long been recognized as said in the old documents “If you can find a thousand years old lingzhi on an old Mulberry tree, you can save a dying person”.

Only natural ones are genuine Phellinus linteus.” Phellinus linteus grows naturally in trunks of willow, paper mulberry and elm tree that is more than 100 years old, and shall grow for minimum 30 to 40 years to make a fruit body being used for medical application. In addition, the growth conditions such as humidity, temperature and lighting are very delicate, so that Phellinus linteus is very rare in the nature. That is the reason why, it is almost impossible to collect and take a fruit body in the nature.

In the tradition Chinese medicine, Sang Hwang (Phellinus linteus) was classified as Lingzhi or Reishi. Sang Hwang (Phellinus linteus) is the most highly rated herb category in terms of multiple benefit and absence of side effects.

Sang Hwang (Phellinus linteus) ranked number one of the superior medicines, is the most exalted medicine in ancient times and has been used for perpetual youth and longevity. All observations show that Sang Hwang (Phellinus linteus) has no side effects and can be consumed in high dosages and in parallel with other medications.

Sang Hwang (Phellinus linteus) has been revered as herbal medicines for thousands of years in China and Japan. Emperors of the great Chinese Dynasties and Japanese royalty drank tea and concoction of the Sang Hwang (Phellinus linteus) for vitality and long life.

It positively affected the life energy or qi of the heart, repairing the chest area and benefiting those with a knotted and right chest. He wrote that it also increased intellectual capacity and banished forgetfulness. Taken over a long period of time, ability of the body would not cease and the years would be lengthened to those of the immortal fairies.

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So if this is a mushroom found rarely even in Asia, then how did it end up in the American wild? Or is there an American variety, too?

I don't want to rain on anybody's parade but there are a lot of shelf fungus/polypore type mushrooms that look like that and your picture doesn't even begin to have enough detail to identify that one. In fact, it's pretty hard to ID fungus just from pictures and you should NEVER eat a mushroom you've just identified from a photo.

I googled around at some of the sites I use to look up fungus and I don't see anything called Phellinus linteus, which says to me either it doesn't occur here (in the US) or that's not the currently accepted scientific name (and I have to say that the one website you linked to may be talking about Phellinus but the photo is looks like a dried shiitake mushroom floating in a glass of tea or something -- it certainly isn't a Phellinus, which has pores instead of gills and doesn't have a stem like that - just saying those sites aren't good for identification purposes).

There are some Phellinus listed on mushroomexpert.com andGary Emberger's 'Fungus growing on wood' site but I don't know that any of them are what you've got (the Emberger site is more for the northeast than your part of the country).

A lot of mushroom identification books I see here are actually European; we assume that the species are the same here but it's not necessarily true; same with Asian species. It's harder to ID fungus than most flowering plants and I think the work just hasn't been done to say for sure one way or the other that the species are the same.

Blakrab, I also poked around the Internet. Several other genera are saprobes with that general appearance. When saltcedar replied to your original post, 4 years ago, he suggested Phellinus as one locally-existing saprobic. However, there seem to be many other genera with similar appearance in that group. If you want a more specific answer than provided by saltcedar and weedwoman, you might search for "Texas mushroom groups", and then ask them for help with your photo. One possible resource would be Texas Wild Mushrooming, but there are lots of other mycology clubs in your area.

Good lord, I didn't even notice the date of the original post.

In my experience local mushroom clubs are more interested in edibles than woody shelf fungus, but it's worth a try, especially if it's something locally common. If you think it's killing your tree you might also try the county extension agent or whoever deals with that sort of thing down there.