Horehound (marubium vulgare)
Horehound is a type of mint with white flowers. It is a medicinal herb that activates the immune system and is useful in clearing congestion. Horehound is a legendary herb among many different cultures around the world. Its most famous use is in the making of cough drops and candies, but horehound can also be used in teas and tinctures.
Native to Eurasia and North Africa, horehound is also naturalized throughout North and South America. It is likely the original bitter herb used in Passover seders.