Twilight of the Gods
Alchemical creations and materials have to be handled on a one at a time basis. Alchemists will not normally function outside of major cities, and are even more rare than arcane and divine casters. Herbalism developed in all cultures, but the science of alchemy is largely limited to Christian lands, originating from the lore of Greece and Rome, and before that, Egypt.
Knowledge of herbalism and the ability to use it to heal is represented by the Medicine skill, as one might expect. If one does not have proficiency in Nature, Medicine can also be used to identify and harvest medicinal plants and animal parts.