Hello! While the flora is technically specific to the Feywilds, Claude's expertise combined with the fact that he's been in the Feywilds before can allow him to make reasonable educated guesses. You can incorporate the fact that he might be incorrect in certain cases how you wish!

Antidotes can be used! They might not be as effective against stronger poisons, but you're free to determine the efficacy based on your goals in the thread.