The tree whose bark contains quassinoids used for antimalarial research and traditional remedies is Quassia.
The clue primarily points to Quassia amara, a small tropical tree in the family Simaroubaceae. Its bitter wood and bark contain quassinoids, including quassin and related compounds. These chemicals are responsible for the plant’s intensely bitter taste and have attracted interest for antimalarial, insecticidal, anti-inflammatory, and antiparasitic effects.
Quassia has a long history of use in tropical medicine. Bark and wood extracts have also been used as flavoring agents and as botanical insecticides. Research on compounds from Q. amara has identified molecules such as simalikalactone D with activity against malaria parasites, although a laboratory or traditional-use claim should not be confused with a replacement for proven antimalarial treatment.
Cinchona is the most common mix-up: its bark is famous for quinine, a different antimalarial compound. Neem and Artemisia also have medicinal reputations, but they are not the source indicated by the quassinoid clue.