One of my parents' friends is a landscape architect and is therefore a "plant person" in the most genuine sense. According to him, you either are or you aren't. The good thing is, it can be developed, you don't have to be born with it. He even said that he has included certain plants and trees in his will as he has become more and more attached to them over the years- in some cases more than 20 years- and he wants to know they will be taken care of even if he can't be the one to do it. He had this idea because he noticed that when people were in his house they could walk by a dying plant and not even realize it was dying... and when you put it that way, it's sad.
A little intense? Sure, but after talking to him I have started to notice plants and flowers much more. When you look at the intricate details of a flower or sit beneath huge old oak trees and really think about them, it's hard not to become a "plant person" yourself. I mean, some flowers only live for a day- what's the purpose in them being so beautiful? And some trees have been around forever and will be there even when your gone.
..And come to think of it, I'm pretty sure I have quite a few friends who are plant people.