The Oaken Ring can be worn only be druids. The ring offers no special abilities, but it can be used to let Cespenar create the Heartwood Ring which also requires a Nymph's Tear and some gold. This item appears in Baldur's Gate II: Throne of Bhaal and Baldur's Gate II: Enhanced Edition.
It can be gained from the Priest of Waukeen oustide in Amkethran if you save him or gained off his body if you let the Monk kill him.
|“||This ring is fashioned not from gold or precious metal, but from simple oak.||”|