Your summoned vines have thorns.

Prerequisites: None

Benefit: A thorny spell must be a plant spell that has a duration of multiple turns and modifies an area. When creatures move in a thorny spells area, they take 2d6 points of piercing damage for each level increase of the spells level. The woodland stride ability protects individuals from the damage. Furthermore, entangled creatures take the damage even without moving.

A thorny spell uses up a spell slot one level higher per level of thorns.