Saponins (Latin "sapon", soap + “-in", one of), also referred to selectively as triterpene glycosides, are bitter-tasting usually toxic plant-derived organic chemicals that have a foamy quality when agitated in water. They are widely distributed but found particularly in soapwort (genus Saponaria), a flowering plant, and the soapbark tree ("Quillaja saponaria"). They are used in soaps, medicinals, fire extinguishers, speciously as dietary supplements, for synthesis of steroids, and in carbonated beverages (the head on a mug of root beer). Structurally, they are glycosides, sugars attached to another organic molecule, usually a steroid or triterpene, a steroid building block.