The origins as to why the thistle became a national symbol in Scotland are unknown. One story holds that a party of Scottish warriors suffered a Viking attack while sleeping and were only saved as one of the Vikings stepped on a thistle with bare feet. The Vikings screams woke the other sleeping Scots, and the Scots won the battle. Legend holds that the thistle became known as the “Guardian thistle” after that day and was adopted as a symbol of Scotland. No historical evidence exists to back up this story, and even the type of thistle used as a symbol varies.
Read more: What Are the Scottish Symbols? | eHow.com http://www.ehow.com/info_8097829_scottish-symbols.html#ixzz1w0DPmN6z