Three species of duckweed (Lemna minor, Lemna trisulca, and Spirodela polyrhiza) have all been used in western herbal medicine and as a food source.
Since common duckweed (Lemna minor) is the most common, it is very likely it is the species referred to in earlier herbal literature.
Pedanius Dioscorides (1st century AD) recommended duckweed against St. Anthony’s fire (Erysipelas).
Henrik Smith (1495 – ca. 1563), a Danish humanist and a doctor, mentioned the herb in his writings where he writes that it can be used as a preventative measure against plague-like diseases.
Simon Paulli (1603 – 1680), a Danish physician and naturalist, wrote that the herb could be used by women if they suffered from headaches due to overexposure to the sun. They should then enclose it in a linen cloth and place it on the forehead.
Duckweed is considered to have an inflammatory and diuretic effect, which is partially due to the flavonoid content.
Today it is used internally, often in combination with other medicinal herbs, to treat inflammation of the upper respiratory tract, and as a anti-inflammatory and blood purifying remedy for chronic rheumatic ailments such as rheumatoid arthritis and osteoarthritis (OA).
Externally, it has been used to treat skin rashes, eczema, swellings and insect bites, usually in the form of a poultice.