This introduction from Asia or North America grows at the edges of slow moving or still water. It is a shy flowerer so you can often find only the leaves which are light green with one edge wrinkled. The reason it is Sweet-flag is that the leaves look a little like those of the Yellow flag but not much. When crushed they smell sickly sweet.

It is found throughout England and in east Wales but is less common in Scotland and uncommon in Ireland.