Which tree's bark provides the antimalarial drug quinine?

Cinchona is the tree genus whose bark provides the antimalarial drug quinine.

Cinchona trees and shrubs are native to tropical Andean forests in western South America. Their bark contains several medicinal alkaloids, including quinine, quinidine, cinchonine, and cinchonidine. Quinine became historically important because it could treat malaria, a disease that was widespread in tropical regions and once especially deadly to Europeans working overseas.

Spanish missionaries encountered cinchona bark in South America during the 17th century, and the remedy became known in Europe as Peruvian bark or Jesuit’s bark. French chemists Pierre Joseph Pelletier and Joseph Bienaimé Caventou isolated quinine from cinchona bark in 1820, turning a traditional bark preparation into a defined chemical drug.

The answer is a genus rather than one universally agreed species: several Cinchona species have supplied quinine. Cinchona ledgeriana, now generally treated within Cinchona calisaya, became especially valuable because cultivated bark could contain high quinine levels. Quinine is also the bitter flavoring associated with tonic water.