A "giant cannibal plant" was one of the native plant life forms of the planet K-G.
History and specifics[]
The giant cannibal plant fed by generating an internal vacuum which sucked its prey into its maw. It was called a cannibal not because it ate its own kind, but because it ate Humans. However, the plant displayed aggressive behavior towards other giant plant lifeforms as well.
In the year 2266, a cannibal plant attempted to eat a Starfleet landing party from the Federation starship USS Enterprise, but were rescued by Crewman Hunt. Hunt, who had been transformed into a plant himself, retained enough intelligence to attack and kill the cannibal plant at the cost of his own life. (TOS comic: "The Planet of No Return")