Plant Family
Polygalaceae
The milkworts — pea-like flowers on unrelated plants, and roots whose saponins have been official expectorants for two centuries.
A widespread family of herbs and shrubs whose medicinal members are saponin-rich roots, used as reflex expectorants in western pharmacy and as tonics in Chinese practice.
5 Notable Members
Overview
The Milkwort Family
Around 1,000 species of herbs, shrubs and a few trees, distributed almost worldwide. The flowers are a well-known piece of botanical mimicry: they look convincingly pea-like, with what appear to be wings and a keel, and the family is entirely unrelated to the legumes. The apparent wings are sepals, and the keel often carries a fringed crest found nowhere in Fabaceae.
The name means much milk — from a classical belief that grazing on the plants increased milk yield in cattle, a use that has not survived scrutiny but has left its trace in milkwort.
Shared Traits
How to Recognise It
In Practice
Medical Significance
The family’s medicine is root medicine, and it is saponin medicine.
Senega — Seneca snakeroot — was learned from the Seneca people, who used it for snakebite, and adopted into western pharmacy in the eighteenth century for an entirely different purpose. It became a standard expectorant, and remained official in the pharmacopoeias of Europe and North America for around two hundred years, appearing in cough preparations still sold today. Its standing rests on monographs rather than trials: the European and older national monographs document it thoroughly, and controlled clinical evidence is essentially absent.
The mechanism is worth understanding because it is characteristic of the whole saponin-expectorant class. These are reflex expectorants: the saponins irritate the gastric mucosa, and a vagal reflex increases bronchial secretion, thinning mucus so it clears more easily. The action is indirect, which is why the dose is small and why nausea marks the ceiling.
Polygala tenuifolia — yuan zhi — is the family’s other significant member and is used differently. In Chinese medicine it is both an expectorant and a calming and cognitive herb, and it now carries a substantial preclinical neuropharmacology literature.
Saponins are the useful principle and the limiting one. Senega causes nausea, vomiting and gastric irritation at doses not far above the therapeutic range — an inherent consequence of a reflex-mediated mechanism. It is avoided in pregnancy and in gastritis or peptic ulceration, and it is not a herb for casual dosing.
Phytochemistry
Characteristic Chemistry
Triterpenoid saponins are the defining class — the senegins and senegasaponins, built on the aglycone presenegenin, with polygalic acid alongside. The family also produces two more unusual groups: oligosaccharide esters (the sibiricose and tenuifoliside series), which carry much of the neuropharmacological interest in P. tenuifolia, and xanthones.
Methyl salicylate gives senega root its characteristic wintergreen scent, and the sugar alcohol polygalitol is present in quantity.
Beyond the Database
Also in This Family
Notable members without a monograph yet.
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