quassia (kwŏshˈə) [key], name for several tropical trees and for a bitter extract from their bark. The extract containing complex terpenoid compounds called quassinoids is used medicinally as a bitter tonic and a pinworm remedy; it is also used in insecticides, e.g., in flypaper and against aphids. Surinam quassia comes from the tree Quassia amara of N Brazil and surrounding regions; Jamaica quassia comes from Picrasma excelsa of the West Indies. Some Old World quassia species are similarly used. The trees are related to the ailanthus. Quassia is classified in the division Magnoliophyta, class Magnoliopsida, order Sapindales, family Simaroubaceae.