The Charter Oak was an unusually large white oak tree growing, from around the 12th or 13th century until 1856, on what the English colonists named Wyllys Hyll, in Hartford, Connecticut, USA. Its name derives from its importance as a legendary symbol of American independence (specifically, autonomy from England) from the story of how Connecticut's constitutional charter had been hidden within the hollow of the tree to thwart royal-ordered confiscation by English authority. This document is what earned Connecticut its nickname as the Constitution State, and the Charter Oak is commemorated on the Connecticut State Quarter.
http://en.wikipedia.org/wiki/Charter_Oak