Yellow flag is
native to Europe, Great Britain, North Africa and the
Mediterranean region. It is a popular ornamental plant for
wet areas; it escaped from cultivation and is found in
marshes throughout the United States and Canada. Many
states list it as an invasive species because it can crowd out
native pond plants. It is planted in the gardens behind
the Center where it is carefully monitored and controlled.
The roots of
yellow flag are used in folk medicine to treat several ailments,
but all parts of the plant can also cause vomiting and diarrhea.
Flowers are used to make a yellow dye and the roots produce a
dark brown dye.
(Photo credits: Washington
Noxious Weed Control Bureau)