A thorn tree found on Wearyall Hill, near Glastonbury Tor. It blooms twice a year, once in the spring, and once in the winter. Each winter, a blooming sprig is cut and sent to the reigning monarch of England.
The tree--probably originally at the abbey--was a popular pilgrimage site until it was chopped down during the English Civil War by the Puritans, who finished the destruction of the abbey begun by Henry VIII. In the 20th century, a new tree was planted on Wearyall Hill, taken from one of the trees growing throughout the Glastonbury area.
There is a thorn tree growing in the confines of the old abbey; this is also refered to as the Glastonbury Thorn. Which is the "real" tree is irrelevant.