Chances are it is simply some grape vine. As a moderately hard wood, grape vine should be fine in an aquarium setting. I also like the look of that stuff. Since I have wild grapes growing in my woods, I may kill some off and wait for it to dry so that I can use it in my tanks. That picture shows some great wood decor.
you can get sumatara drift wood that looks like that first set of pictures,i have a lump which is quite chunky but when i got it from my lfs they also had thin spindly sections of it.from what i read it grows a form of fugus on it that is good for plecos,my bristle nose and pleco seam to spend alot of time stuck to it!!!