Gildergreen
Gildergreen is the tree outside of the Temple of Kynareth in Whiterun.
When the Dragonborn first enters the city, the tree appears to be dying, but as the priestess Danica Pure-Spring explains, it is merely dormant and requires some Eldergleam Sap to be restored to its former glory. Alternatively, a new Eldergleam Sapling can be planted to replace it.