A human heart made of wood
Found implanted in the chests of suspected servitors of the Primal Gods. In addition those implanted with the Briar Hearts have a root in place of their tongue and they constantly have mud falling from their mouths.
The Briar Hearts are magical and have an aura of Transmutation..
The Briar Hearts feed off the blood and other bodily fluids of the person it is implanted in. When exposed directly to blood a rapid cycle of growth is triggered.
One Briar Heart, when removed from its host for study killed the mage who was examining it. The Briar Heart grew multiple roots and vines and became animate, attempting to kill the adventures that encountered it.
The exact cause of its transformation is unknown.