The leek is one of the national emblems of Wales, worn along with the daffodil (in Welsh, the daffodil is known as "Peter's leek", Cenhinen Bedr) on St. David’s Day. According to one legend, King Cadwaladr of Gwynedd ordered his soldiers to identify themselves by wearing the vegetable on their helmets in an ancient battle against the Saxons that took place in a leek field. The Elizabethan poet Michael Drayton stated, in contrast, that the tradition was a tribute to Saint David, who ate only leeks when he was fasting. Whatever the case, the leek has been known to be a symbol of Wales for a long time; Shakespeare, for example, refers to the custom of wearing a leek as an “ancient tradition” in Henry V. In the play, Henry tells the Welsh officer Fluellen that he, too, is wearing a leek “for I am Welsh, you know, good countryman.” The 1985 and 1990 British one pound coins bear the design of a leek in a coronet, representing Wales.

Alongside the other national floral emblems of countries currently and formerly in the Commonwealth or part of the United Kingdom (including the English Tudor Rose, Scottish thistle, Irish shamrock, Canadian maple leaf, and Indian lotus), the Welsh leek appeared on the coronation gown of Elizabeth II. It was designed by Norman Hartnell; when Hartnell asked if he could exchange the leek for the more aesthetically pleasing Welsh daffodil, he was told no.

Perhaps the most visible use of the leek, however, is as the cap badge of the Welsh Guards, a regiment within the Household Division of the British Army.

In Romania, the leek is also widely considered a symbol of Oltenia, a historical region in the southwestern part of the country. In early 1990s Albania, protestors waved leeks in defiance of the Communists whose policies had virtually reduced many to this staple.