The ''quarantine'' makes no sense
I mean, if you think of it - any wild animal, be it a bird, rodent, bug, lizard can go near to the plants and escape, spreading the plants outside of the ruin.
Unless, of course, this plant ONLY eats human flesh, which is a bit unrealistic - we are after all, mammals ourselves.
On a side note, if the plant is so deadly, why not just cover the entire ruin in gasoline and light it ablaze?