Canticle Bark is a quest item found in The Elder Scrolls V: Dawnguard.
It is a quest item for the quest Unseen Visions. This can be harvested in Ancestor Glade by using the Draw Knife.
If the Dragonborn has the alchemy perk Green Thumb, they can harvest two units of Canticle Bark. One with a value and weight of 0, the other with a weight of 0 and value of 350. However, if both of these Canticle Barks are put into any container and then removed, the one with 0 value and weight will disappear.