It seems like Cycles is totally ignoring my choices of bitmaps. No matter what image file I specify, I get the base color with no texture. The only one that seems to work (sort of) is the “Water rippled” selection from the library.
For example, the attached .jpg seems like it should somehow alter the look of the ground plane, but the attached screen capture shows what I’m getting as a result. I’ve tried it both as a PBR and as a custom material with the same result: