The Soap bark tree (Quillaja saponaria) is an evergreen tree in the family Rosaceae, native to subtropical central Chile. It can grow to 15-20 m in height. The tree has thick, dark bark, smooth, shiny and oval evergreen leaves 3-5 cm long, white flowers 15 mm diameter borne in dense corymbs, and a dry fruit with five follicles each containing 10-20 seeds.

Soap bark tree has a long history of medicinal use with the Andean people who used it especially as a treatment for various chest problems. The saponin content of the bark helps to stimulate the production of a more fluid mucous in the airways, thus facilitating the removal of phlegm through coughing. The saponins of this tree are also considered to have adjuvant properties for vaccine solutions.