Plant Man is an enemy in Final Fantasy Mystic Quest. It attacks in areas near Fireburg, but is itself weak to Fire and Axe attacks. Since both Reuben and Benjamin have access to powerful Axe-type weapons by the time they reach Fireburg, the Plant Man is no threat to them.
In the Japanese release, this creature is known as "Mandrake". Mandragora is a plant belonging to the nightshade family. According to legends surrounding witchcraft, when mandragoras (Mandrake plants) are uprooted, they emit a piercing scream which kills all who hear it.