Terragen has no such options to choose/check. It could be that if you open the saved obj in an app like ZBrush, you might be able to re-establish the parts.
What I would be interested in is how you can 'render the textures onto a 2D image that can be used by other software packages'. I often use generic textures that are called in, but a single combined texture would sometimes be handy to have. Can you expand on that perhaps? What app could do that?
I found these plants for Blender. They are .fbx files, so i load them into blender and save them out as .obj files. The maps come with them. They are 2k, 4k, 8k and 16k.
With watermark, I'm afraid. Can't post without. A Roman road, a sabretooth scene, and a commissioned work showing nature 'enhancement' in an otherwise ordinary meadowland. The latter being too boring to show anyway.