Quassia is the most bitter tasting known plant in the world. This bitterness comes from the phytochemical quassin. When quassin is compared to quinine, another bitter phytochemical, it can be measured as being roughly 50 times more bitter. In small quantities this quality has made Quassia a favourite ingredient in bitters. Quassia is native to the Caribbean and South America and counted as a shrub or small tree. It has beautiful large red blooms and distinctive glossy leaves. Find all our Quassia products below.