On St Patrick’s Day (17 March) Irish people wear shamrock (usually lesser trefoil, Trifolium dubium), which the Saint is said to have used to demonstrate the nature of the Holy Trinity.

This is shown in the image here, part of an 1881 stained glass window in Gloucester Cathedral, in memory of General Sir Joseph Chackwell, who died on 8 April 1859.

Photographed September 2017.

Observation at the London St Patrick’s Day Parade, 17 March 2019:  Apart from a few people, including the Mayor of London, walking at the front of the parade, very few of the other people in the parade and the people watching wore live shamrock, though shamrock motifs were common on hats and other clothing.