Early in the history of Whiterun a piece was grafted from the tree and planted in the city square outside the Temple of Kynareth. This offspring of the Eldergleam Tree is called Gildergreen. Many believe the Eldergleam Tree is the oldest living thing in Skyrim, if not all of Tamriel.
In order to reach Eldergleam one must have the weapon Nettlebane, acquired as part of the first step for The Blessings of Nature quest. Once the Dragonborn reaches the tree he or she can either acquire some sap with the blade, or if the follower of Kynareth, Maurice Jondrelle, tags along, acquire a sapling to bring back to Danica Pure-Spring in Whiterun. Activating the tree will causes several Spriggan to appear.
Once you complete this quest, Nettlebane will contribute its weight into your inventory (10 ).