Although onscreen credits listed producer Philip Yordan as the screenwriter, according to Writers Guild of America (WGA) records, the screenplay was actually written by blacklisted writer Bernard Gordon. Gordon's credit was officially restored by the WGA in 1996.
I have a multi-episode DVD of a British film of this for TV. It's interesting, but I really LOVE the Keel version in color. And the plants are so much fun to watch!