Iris, yellow flag, Iris pseudacorus
Yellow flag grows in damp marshy areas, swampy woods and in shallow water or wet ground on the edges of rivers and ditches. It is often found in shady places. The plant succeeds in water up to 15cm deep.
A slice of the root held against an aching tooth is said to bring immediate relief.
It was at one time widely used as a powerful cathartic but is seldom used nowadays because of its extremely acrid nature.
It can also cause violent vomiting and diarrhoea.
When dried the root loses its acridity and then only acts as an astringent.
A beautiful yellow dye is obtained from the flowers. A good black dye is obtained from the root if it is mixed with iron sulphate. It is brown otherwise.
The root is a source of tannin and has been used in making ink.
A delicately scented essential oil, obtained from the roots, has been used to adulterate the oil of Acorus calamus.