A boutonnière is a floral decoration worn by men, typically a single flower

Flower

A flower, sometimes known as a bloom or blossom, is the reproductive structure found in flowering plants . The biological function of a flower is to effect reproduction, usually by providing a mechanism for the union of sperm with eggs...

 or bud. The word comes from the French

French language

French is a Romance language spoken as a first language in France, the Romandy region in Switzerland, Wallonia and Brussels in Belgium, Monaco, the regions of Quebec and Acadia in Canada, and by various communities elsewhere. Second-language speakers of French are distributed throughout many parts...

 word for buttonhole, which is the British

British English

British English, or English , is the broad term used to distinguish the forms of the English language used in the United Kingdom from forms used elsewhere...

 term.

While worn frequently in the past, boutonnières are now usually reserved for special occasions for which formal wear

Formal wear

Formal wear and formal dress are the general terms for clothing suitable for formal social events, such as a wedding, formal garden party or dinner, débutante cotillion, dance, or race...

 is standard, such as at prom

Prom

In the United States and Canada, a prom, short for promenade, is a formal dance, or gathering of high school students. It is typically held near the end of the senior year. It figures greatly in popular culture and is a major event among high school students...

s, homecoming

Homecoming

Homecoming is the tradition of welcoming back alumni of a school. It most commonly refers to a tradition in many universities, colleges and high schools in North America...

s, funeral

Funeral

A funeral is a ceremony for celebrating, sanctifying, or remembering the life of a person who has died. Funerary customs comprise the complex of beliefs and practices used by a culture to remember the dead, from interment itself, to various monuments, prayers, and rituals undertaken in their honor...

s, and weddings. (Women who wear jackets on these occasions also often may wear 'buttonholes', but more typically a woman would wear a corsage

Corsage

Corsage refers to a bouquet of flowers worn on a woman's dress or worn around her wrist.* Corsages are often worn by the mothers and grandmothers of the bride and groom at a wedding ceremony in some countries....

.) Nowadays, a lapel pin

Lapel pin

A lapel pin is a small pin often worn on the lapel of a dress jacket. Lapel pins can be purely ornamental or can indicate the wearer's affiliation with an organization or cause; for example, American Flag lapel pins became very popular in the United States, especially among politicians, following...

 is worn more often than flowers on business suits.

Practice

Traditionally, a boutonnière was worn pushed through the lapel

Jacket lapel

Jacket lapels are the folded flaps of cloth on the front of a jacket or coat, and are most commonly found on formal clothing and suit jackets. Usually they are formed by folding over the front edges of the jacket or coat and sewing them to the collar, an extra piece of fabric around the back of the...

 buttonhole (on the left, the same side as a pocket handkerchief

Handkerchief

A handkerchief , also called a handkercher or hanky, is a form of a kerchief, typically a hemmed square of thin fabric that can be carried in the pocket or purse, and which is intended for personal hygiene purposes such as wiping one's hands or face, or blowing one's nose...

) and the stem is held in place with a loop at the back of the lapel. The flower's calyx

Sepal

A sepal is a part of the flower of angiosperms . Collectively the sepals form the calyx, which is the outermost whorl of parts that form a flower. Usually green, sepals have the typical function of protecting the petals when the flower is in bud...

, if pronounced such as those of a carnation, should be fully inserted into the buttonhole which would secure it tightly and flat against the lapel. Thus the buttonhole should ideally be at least 1⅛" long for there to be enough room to fit a standard sized flower's calyx. Otherwise, the calyx would not fit into the buttonhole and the flower head would hang freely and move about in the wind.

However, on many recently made coats and jackets, the lapel is made without the loop required, which would normally sit on the reverse of the lapel, beneath the buttonhole. Sometimes, the lapel buttonhole is in the 'keyhole' shape, as opposed to the traditional straight cut, or is not even pierced through, in which case the boutonnière may be pinned onto the jacket lapel, although this may be considered unsightly and continued pinning could eventually damage the cloth or silk facing.

Flowers

The flower itself is often a carnation

Carnation

Dianthus caryophyllus is a species of Dianthus. It is probably native to the Mediterranean region but its exact range is unknown due to extensive cultivation for the last 2,000 years. It is the wild ancestor of the garden carnation.It is a herbaceous perennial plant growing to 80 cm tall...

, of which the most formal is white. The classic alternative is one in clove red. Other colours and flowers may also be chosen to better coordinate with whatever else is being worn, such as a blue cornflower. A white gardenia is sometimes seen as a superior alternative to carnations given its scent and beauty.

Traditionally, certain flowers are associated with certain events, people or days:

• Red roses
  Roses
  Roses is a municipality in the comarca of the Alt Empordà in Catalonia, Spain. It is situated on the coast at the northern end of the Gulf of Roses, and is an important fishing port and tourist centre. The C-260 road links the town with Figueres....
  
   are worn by Englishmen on St. George's Day
• Blue cornflowers are often worn by Old Harrovians
• Primroses
  Primula vulgaris
  Primula vulgaris is a species of Primula native to western and southern Europe , northwest Africa , and southwest Asia...
  
   are worn for Disraeli's birthday
• Artificial poppies (mostly red) are worn for Remembrance Day
  Remembrance Day
  Remembrance Day is a memorial day observed in Commonwealth countries since the end of World War I to remember the members of their armed forces who have died in the line of duty. This day, or alternative dates, are also recognized as special days for war remembrances in many non-Commonwealth...
  
  
• Orchids are associated with Joseph Chamberlain
  Joseph Chamberlain
  Joseph Chamberlain was an influential British politician and statesman. Unlike most major politicians of the time, he was a self-made businessman and had not attended Oxford or Cambridge University....
  
  
• Green carnations
  The Green Carnation
  The Green Carnation, first published anonymously in 1894, was a scandalous novel by Robert Hichens whose lead characters are closely based on Oscar Wilde and Lord Alfred Douglas - also known as 'Bosie', whom the author personally knew...
  
   are sometimes associated with homosexuality
  Homosexuality
  Homosexuality is romantic or sexual attraction or behavior between members of the same sex or gender. As a sexual orientation, homosexuality refers to "an enduring pattern of or disposition to experience sexual, affectional, or romantic attractions" primarily or exclusively to people of the same...