Common Soapwort (Saponaria officinalis) is a vespertine flower, and a common perennial plant from the carnation family (Caryophyllaceae). Other common names are Bouncing Bet and Sweet William; locally it is simply "the Soapwort" although there are about 20 species of soapworths altogether.
The scientific name Saponaria is derived from the Latin sapo (stem sapon-) meaning "soap," which, like its common name, refers to its utility in cleaning. From this same Latin word is derived the name of the toxic substance saponin, contained in the roots. It starts producing a lather when in contact with water. The epithet officinalis indicates its medicinal functions.
The plants possesses leafy, unbranched stems (often tinged with red) grow in patches, attaining a height of 70 cm. The broad, lanceolate, sessile leaves are opposite and between 4 and 12 cm long. It's sweetly scented flowers are radially symmetrical and pink, or sometimes white. Each of the five flat petals have two small scales in the throat of the corolla. They are about 2.5 cm wide. They are arranged in dense, terminal clusters on the main stem and its branches. The long tubular calyx has five pointed red teeth.
Despite its toxic potential, soapwort finds culinary use as an emulsifier in the commercial preparation of tahini halva, and in brewing to create beer with a good "head". In India, the rhizome is used as a galactagogue.