Green Thing

1st app.-

Looking to prove plants have intelligence, a scientist set out for a remote island to test the serum out on the plant species ignatius rex. Not finding a specimen and not wanting to waste the trip, he injected a weed instead. The weed grew into a monstrous being which began to chase the man. He finally stumbled upon the plant he'd been searching for, and upon administering the serum to it, it grew and slew the weed.
The Rex plant then opted to remain on the island, and bid the man no longer experiment on plants.

Credit - The Monsters of Jack Kirby