Yes, primarily image 18, although also the flower stalks (?) in 19-21. Regarding the tree trunk in 18, I would say that it may be realistic for it to be so smooth, but what we see in that image are then two problems. 1: the join of the branch to the trunk (which I think could be somewhat hidden with rougher bark on the trunk), and 2: the overall low resolution of the base texture for the trunk, as there is some detail there but it is blurry. A smooth trunk in real life may have little detail, but what it does have is of "fine" detail so to speak. I think you could probably improve this just by adding a very subtle Power Fractal noise detail to the trunk texture.
- Oshyan