While Briars spells fall under the Aberrant sorceries used by exiled criminals, Impenetrable Thorns and Mantle of Thorns are derived from the Scadutree of the Shadow Realm.

With arrows and with bows shall men come thither; because all the land shall become briers and thorns. And on all hills that shall be digged with the mattock, there shall not come thither the fear ...