Soap Plant, a name applied to various plants that contain substances called saponins in their roots, bulbs, leaves, stems, bark, or fruit. Saponins are water soluble and form a rich, soapy lather when shaken with water. Saponins are used as detergents and as soap substitutes that are mild enough for washing delicate fabrics such as silks and woolens. Saponins are also used in the preparation of hair tonics and medicines, as foaming agents in fire extinguishers, and as emulsifiers of fats and oils.
Among the soap plants used as commercial sources of saponins are the soapwort, or bouncing bet (a perennial herb native to Eurasia and a member of the pink family); the soapbark tree (an evergreen native to Chile and a member of the rose family); and the soapberry tree (a small, tropical American tree of the soapberry family).
The soapwort is Saponaria officinalis. The soap-bark tree is Quillaja saponaria. The soapberry tree is Sapindus saponaria.Soapberries contain saponins, which are water soluble and form a rich, soapy lather when shaken with water.