Thistle is the common name of a group of flowering plants characterised by leaves with sharp prickles on the margins, mostly in the family Asteraceae. Prickles often occur all over the plant – on surfaces such as those of the stem and flat parts of leaves. These are an adaptation that protects the plant against herbivorous animals, discouraging them from feeding on the plant.
The thistle has been the national emblem of Scotland since the reign of Alexander III (1249–1286) and was used on silver coins issued by James III in 1470. It is the symbol of the Order of the Thistle, a high chivalric order of Scotland. It is found in many Scottish symbols and as the name of several Scottish football clubs. The thistle, crowned with the Scottish crown, is the symbol of seven of the eight Scottish Police Forces (the exception being the Northern Constabulary). The thistle is also the emblem of Encyclopædia Britannica, which originated in Edinburgh, Scotland. Carnegie Mellon University features the thistle in its crest in honor of the Scottish heritage of its founder, Andrew Carnegie.
According to a legend, an invading Norse army was attempting to sneak up at night upon a Scottish army's encampment. During this operation one barefoot Norseman had the misfortune to step upon a thistle, causing him to cry out in pain, thus alerting Scots to the presence of the Norse invaders.
The thistle features in the song The Thistle o' Scotland which uses the plant as a humorous metaphor for the prickly determinations of the Scots: Wha daur meddle wi' me! which is the Scots translation of the motto, Nemo me impune lacessit.