What about mushrooms? What about slime molds? What about insects? Google Lens does all of the above as well as plants and flowers and fruit and shoes. I think PlantNet looks nice, and I appreciate the web-only version! But Lens is built into my camera, it's hard to beat.

What I think would be useful is an app that could diagnose problems with plants. Some get yellow when dry, some get yellow when too wet. You could tell it the species and it could compare it to training data of sick plants of that species.