Plant at the heart of pagans' peerless medicine (6)
I believe the answer is:
garlic
'plant' is the definition.
(garlic is a plant)
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for garlic that I've seen before include "Aromatic bulb used as seasoning" , "Strong-tasting onion-like plant, bad for vampires" , "Vegetable" , "Bulbous herb used in cooking" , "Pungent plant" .)