you didnt get that part?? you should pay better attention to the movie

maybe go see it again.
i believe plants can communicate, just the only way we can realize communication is by vocalization sounds by which our throats make lol. its true though that plants evolve just to protect itself from predators. life evolves to survive. thats what freaked me out the most about this movie, not cuz of the scenes of people killing each other, but just the possibility that, hey, nature could do that to us. if the human race is a potential danger to nature (which it kinda is right now), it will do something in order to get rid of it.
the reason why it was in one small area was just like they said in the movie, a "warning". they explained in the film about how some germs suddenly appeared in the ocean that were gone like a billion years, and then disappeared you know, what was it, the "red wave".
and for it starting it in another country, it explained near the ending on that tv interview that the scientists "theory" about plants rapidly evolving to take out the human race as only credible if it occured somewhere else, instead of just the Northeast of the US, cuz it could have been an outbreak of something, and they explained about CIA buildings there and government testing, so no one really "believed" in that.
overall freaky movie, just cuz of its not impossible for it to happpen

(get it, happen, ha haa)