Manduverac, (manducans veru acidum, eating spit acid) Manduverac is a plant that attacks with its mouth. It generates acid that can be spat out to disinegrate metal. (armor reducing attack) It does no harm to skin or flesh, and is safe to ingest. It also bites things that come near, or eat insects that fly nearby. They open their mouth wide before biting, and after a brief delay, chomp down with all their might. If they hit something, it does massive damage to whatever it hit. If they miss, they take a lot of damage and is unable to attack for a while.
I think the idea of a hostile plant is good, but perhaps it could be almost identical to nearby non-agressive plants so that its attacks would be sneaky.