This spell functions like entangle, except as follows.
The entangling plants are changed to tangled briars covered with sharp thorns that grow to a height of 6 feet.
Each entangled creature takes 1d8 points of piercing damage +1 point per two caster levels in the round it becomes entangled.
In each subsequent round that it attempts to break free or move within the briars, it takes a like amount of damage.
An entangled creature attempting to cast a spell within the briars must make a successful Concentration check (DC 20 + the spell's level) or lose the spell.
The briars are thick and tall enough to grant cover to creatures within or behind them.