Polygala is a large genus of flowering plants which are commonly known as snakeroots or milkworts and are members of the Polygalaceae family. More than 700 species have been described and the genus shows an intercontinental geographical distribution with representatives native to the Americas, Asia, Africa and Australia. The life forms include shrubs, vines and trees which are characterised by having twisted and conical roots which possess a pungent taste and give off a somewhat woody odour reminiscent of wintergreen (Gaultheria spp).
The best known representative of the snakeroots is Polygala Senega L. This plant is native to North America where it is chiefly found in southern Canada and the central and eastern United States. The plant is more commonly known as Seneca snakeroot or simply Senega root, the former of which is derived from the Seneca tribe, Native Americans who used the root to treat snakebite.
The root has been popular in traditional North American herbal medicine where it was used as an expectorant, diuretic, as well as an anti-inflammatory and a medicine to treat toothaches. The root appeared in Europe in the 1700s and was a popular product sold by pharmacists. It is still used in herbal medicine today mainly for its expectorant properties so it’s indications are for respiratory complaints. It is thus an ingredient of cough syrups, teas, lozenges and gargles.
Canada is the chief exporter of the herbal drug and accounts for about 75% in the international trade of this species. This has caused concerns about overexploitation as the root is primarily harvested from the wild. As a result alternative species such as P. tenuifolia Willd. are cultivated on a commercial scale in the Far East, primarily in China and Japan for export to the Western markets. This situation has resulted in pharmacopoeias such as the Ph. Eur. prescribing that the herbal drug Polygalae radix can consist of the dried roots of Polygala senega or of certain other closely related species or a mixture of these Polygala species.
There are two main official herbal drug preparations containing Senega root namely Senega Liquid Extract BP1980 and Concentrated Senega Infusion BP1980. Senega extracts are present as an API in a number of traditional herbal medicinal products (THRs) such as Napiers’ Herbease Chesty Cough Lozenges, Box Herbals Cough & Chest Lozenges, Potters Chest Mixture and Napiers Herbal Cough and Chest Syrup. These licenced medicines can be used to provide relief from sore throats and chesty coughs based on traditional use only.
The active constituents believed to be responsible for the therapeutic properties of the herbal drug are saponins. Saponins are either steroidal (4 membered ring aglycone) or triterpenoid (five membered ring aglycone) glycosides and thus have both hydrophilic (glycoside portion) and hydrophobic (aglycone portion) moieties. This gives them detergent like properties and they form a soapy like foam when present in aqueous solutions.
A complex mixture of bidesmosidic saponin glycosides have been identified in the root of P. senega which are based on the aglycone presenegenin (1). Some of the identified compounds include E-senega saponins a and b, Z-senega saponins a and b, Z-senegins II and III together with senegins II and III. The saponin profile of both P. senega and P. tenuifolia are reported to be similar. These compounds are believed to act by causing local irritation to the gastric mucosa which in turn induces a reflex increase in bronchial secretion, thus reducing the viscosity of the mucus and facilitating its removal by coughing.
Ransom Naturals Ltd manufactures a number of herbal drug preparations containing Senega root namely SE/34 – EFM (Extract for Making) Concentrated Senega Infusion BP1980, SE/27 – EFM Senega Liquid Extract BP1980 and a number of bespoke liquid extracts prepared from Senega root.