Before Swamp Thing, before Man-Thing, there was "The Green Thing". A 13 page Kirby/Ayers cover story in this issue of TALES OF SUSPENSE, featuring a scientist who goes to a remote island to test his serum, which he thinks will increase the intelligence of plants. Not finding the highly developed plant he hopes, he instead tries the serum on a weed, which grows to giant size, gains intelligence and plans to rule the world.
Fortunately, with the remaining serum, the scientist is able to bring a sample of his original choice, Ignatius Rex (and while checking to see if that was a real plant, all I found were links to websites about this story), which is a more benevolent walking plant. Lucky that worked out.
Hm, giant weed turning its own fibres into a lasso, these are some strange comics.
Published July 1961