Target creature you choose within range must succeed on a con save or have its veins erupt with tiny thorns. On a fail, the target takes 4d6 necrotic damage at the end of each of your turns plus the total damage dealt by the spell on the previous turn. The spell ends if you take more than 10 damage or can't see the target.   Ex: if Carion thorns deals 18 damage on turn 1, it will deal 18 + 4d6 damage on turn 2.
Let's say turn 2 deals 18+12, turn 3 is 30+4d6.