Poison Ivy is a pretty good name for a botanically themed villain. Unfortunately, not too many others have been able to come up with anything nearly as intimidating, least of all the one who attacks with pollen and calls himself Plant Master. Speaking of the Plant Master, this guy is an actual villain from the comics who is also known as the slightly snazzier Floronic Man or Floro for short. You may remember him from such films as Batman and Robin in which he was depicted as the scientist responsible for the creations of both Bane and Poison Ivy.
