The Yellow Fag is a popular perennial plant in County Mayo. It can be found in damp grassland, at the edge of lakes, ponds or on river banks. It has long sword like leaves and big bright yellow flowers with purple veins coming into flower from May to July. It grows to 40-150 cm tall.

The plant spreads quickly growing both from new seeds and rhizome. Each winter the plant dies back but in early spring the leaves grow up again from the rhizome.

In the past the rhizome was used as a medicine to cure toothache, cramp or stomach bugs. Also the flowers were used to make a yellow dye, while a black dye was made from the rhizome.

Its botanic name is Iris pseudacorus, in Irish it is called Feileastram.