The genus was first published in Carl Linnaeus's book Species Plantarum ed.

[1] The genus was named after a former slave from Suriname, Graman Quassi in the eighteenth century.

[3][4] Then in 2007, DNA sequencing, and phylogenetic analyses was carried out on members of the Simaroubaceae family.

[1] Countries and regions where species are native include: Andaman Islands, Angola, Bangladesh, Belize, Benin, Bismarck Archipelago, Borneo, northern and northeastern Brazil, Burkina, Cabinda, Cambodia, Cameroon, Central African Republic, Chad, Colombia, Comoros, Congo, Costa Rica, El Salvador, Equatorial Guinea, Gabon, Gambia, Ghana, Guatemala, Guinea, Guinea-Bissau, Gulf of Guinea Islands, Honduras, India, Ivory Coast, Kenya, Laos, Leeward Islands, Liberia, Madagascar, Malaya, Mali, Central, Southeast and Southwest Mexico, Myanmar, New Guinea, Nicaragua, Niger, Nigeria, Northern Territory, Panamá, Philippines, Queensland, Senegal, Sierra Leone, Solomon Islands, Sri Lanka, Sudan, Sulawesi, Sumatera, Tanzania, Togo, Trinidad-Tobago, Uganda, Venezuela, Vietnam, Windward Islands, Zambia, and Zaïre.

The plant is naturalised in the following places: Cuba, Dominican Republic, Haiti, Jamaica, Jawa, and Puerto Rico.

The only accepted species of the genus, by Plants of the World Online as of November 2023 is: Quassia amara L.[1] Although World Flora Online accepts 16 species;[6] There are also taxa that have not been assigned a formal status: The genus has been verified by the United States Department of Agriculture and the Agricultural Research Service (Germplasm Resources Information Network) and they only list 6 species; Quassia amara, Quassia cedron (syn.