I've seen quite a few tree limbs in southwestern Pennsylvania with this smooth, black-like tar on the surface. I believe it is a fungus and not lichen. Does anyone know what species of fungus it is?
You're right though, it is a fungus, and I think I can see the teeny pimple like projections from the surface often characteristic of an ascomycete. It might be a Hypoxylon species (carbon cushions) or relative, but it is flatter than the usual Hypoxylon. Lichens are fungi as well, and there are a few black crustose (flat) ones that look like this, but none I'm personally familiar with that would grow on branches like that. I'm going to flip through some books and if I find it I'll get back to you, unless someone else beats me to it :-)
Well, I don't think certain ID will be possible without someone examining this microscopically, and working on it. The genus Hypoxylon seems likely, or possibly Vivantia. The flatness and shiny-ness I think are significant characters from a macro point of view. Here are a couple of webpages for reference: http://mycology.sinica.edu.tw/xylariaceae/default.asp http://www.forestryimages.org/browse/detail.cfm?imgnum=1504079 Thanks for giving me something cool to puzzle over!