Using it for plant identification is fine as long as it's an AI designed/trained for plant ID (even then don't use it to decide if you can eat it). Just don't use an LLM for plant ID, or for anything else relating to actual reality. LLMs are only for generating plausible-sounding strings of text, not for facts or accurate info.
Best and easiest way is to reverse image search from a photo, it's easy to look through the results for yourself and see what actually matches (it's frequently not the first search result). Perhaps there's some kind of AI involved in reverse image search, but searching like this is infinitely preferable to me instead of some bot telling me an answer which may or may not be correct. It's not "convenient" if you actually care about the answer.
Tbh anything that can give you a curated set of options, and some resources that can help you make the final decision is pretty incredible. But that's the thing about most AI - it needs some human vetting for good results, regardless of how powerful it is
Expert level mushroom identification is a skill and I wouldn't recommend anyone use those apps and assume a mushroom is correct. (And especially don't eat it without absolutely verifying)
Plant identification - not concerned. Most normal people aren't ingesting a plant in the wild. And I mean if you're rubbing against a plant and get a reaction, ideally that's a lesson you only learn once.