Sustarre's Transformation

This potent transformation will polymorph one or more living creatures (as per the polymorph other spell), causing them to take root and turn into trees unless a successful saving throw vs. polymorph is made. Up to twice the caster's level in Hit Dice can be affected, and the caster must select which creatures will be affected. Creatures that successfully save are slowed for 1d4 rounds. A single creature saves at -4, two save at -2, and three or four save at -1. The effect cannot be dispelled, but a remove curse from a caster of higher level than the druid will release a trapped creature. The caster can release any such trapped creature at will.

The material component is mistletoe.