I have often asked myself why men wear flowers in their lapels on their wedding day, but I have never taken the time to look up the history of the wedding boutonnierre. Until today.
Taken from an About Style article explaining the tradition:
Throughout the Middle Ages, a knight going into battle or entering a jousting tournament often donned a token ribbon, scarf, flower or pennant of his lady's family crest over the left arm of his armor, where it was close to his heart.
This is where we get the popular expression, "wearing your heart on your sleeve." Wearing a lady's colors was considered the epitome of chivalry since it signified that he was fighting for her specifically. Modern men have adapted this centuries-old tradition by choosing a flower from the bride's bouquet to pin upon the left lapel of the wedding suit.
French paintings from the mid-16th century depict wealthy men's tunics adorned with a simple arrangement of flowers to represent their political alliances. The boutonniere flourished across Victorian-era England as the Language of Flowers spread. By the 18th century, gentleman strolled down the cobblestoned streets of England with a clipped flower from the garden neatly tucked into the top buttonhole of their frock coats, hence the British name "buttonhole flowers."
Although men had been wearing flowers on their wedding day for centuries already, the boutonniere tradition is often erroneously credited to Prince Albert when he wed Queen Victoria in 1840.
Contemporary grooms prefer a simple single flower or a small bundle of three blooms. The boutonniere can also be embellished with a tiny spray of greenery. Large or spiky flowers are uncomfortable and too heavy, so they are best avoided. The chosen flower should also be represented in the bride's bouquet. Usually, the groom receives a larger version of the boutonnieres that are worn by the other men participating in the wedding. His flowers may also be a different color, such as having the only white rose. Various colors of the same flower are often used to indicate a man's specific role in the ceremony.
Well now I finally know!