Yes, the thistle has been the floral emblem of Scotland since at least the reign of Alexander III (1249–1286). Legend ties its adoption to a Norse invasion foiled when a barefoot attacker stepped on a thistle, alerting Scottish defenders.
The most commonly depicted species is the Scotch thistle (Onopordum acanthium), though the native spear thistle (Cirsium vulgare) is also used.