Dried flowers of camomile.
Camomile has historically been used in beer. Unlike in tea, in which only the flowers are used, in beer the whole plant is used. The bitter taste of the plant goes well in beer, so it is used often by home-breweres and by commercial brewers.
Camomile tea is also said to have a rather medicinal power. In Beatrix Potter's Tale of Peter Rabbit Peter is given camomile tea after being chased by mister McGregor.