Medicinal plants. Branches and flowering parts of three medicinal plants. From left, the plants are: Solomon's seal (Polygonatum biflorum), hawthorn (Crataegus monogyna) and the lily-of-the-valley (Convallaria majalis). Hawthorn and lily-of-the- valley are used as a tonic and diuretic in herbal medicine. Solomon's seal is used as a tonic and as an astringent (to reduce fluid flow).