Boutonnieres is the french word for Buttonholes  and are worn by men on formal occasions, and is traditionally worn on the left lapel of a tuxedo.

The Boutonniere is an important part of the grooms formal ware and is as important as the brides bouquet.  They are usually single flowers and is often a Carnation, however as the groom you and your groomsmen will need to co-ordinate with the rest of the theme.  The grooms boutonniere should however be slightly different to the groomsmen, perhaps using a flower from the brides bouquet.

Here are some ideas of boutonnieres.