This was released in the last few years in Region 1 by the now-defunct DVD label Subversive under the title The Freakmaker with a period tagline billing it as "The 70's Answer To Freaks" I believe. It's a lovely mad-scientist B-film. Find the Subversive release and It even has a replica poster.
Anyway, I remember seeing some still photos of that plant monster in an old monster movie book and thinking they rode a fine line between creepy and ridiculous (I was like 9, what do you expect?).
"Enter a world of the twisted and deformed...a world of monsters and madmen!!"
And here I thought it was going to be a movie about the British Parliament.