What about humans and plants?

Ever since I was very little I have been passionate about myths and legends. I own about 10-13 books about various mythologies and legends from different places. The book that got me into all this was a book about Greek Mythology called "Legendele Olimpului" ("The Legends of Olympus"), which I've read for over 50 times to this day. 

There is one recurring theme in those legends: that of the metamorphosis of a human into a plant, usually a girl trying to escape a god. (Seriously, Greek gods were horrible.) 

I can't say I get it, though, since, in most cases, there would have been other, more logical means of escape. For example, in one of my favourite legends, the god Pan falls in love with the nymph Sirinx, the daughter of the Ladon river. One day she runs scared from the god until she gets to the banks of the very river her father patrons with the god catching up with her. Somehow, she considers herself unable to continue forward and asks her father and her sisters for help. Then she gets turned into a reed. The god cries after her and makes a panpipe using pieces of reed. And that's why the panpipe is called a syrinx and a reed pipe. I must ask: why did she have to turn into a tree? Couldn't she have been transformed into, say, a fish and be together with her family? Or a mer... oh, ok, not a mermaid since the greek didn't have that. Still, you get my point. Or why couldn't the spell be reversed?

See, always the story ends here. The human gets turned into a plant, end of story. Why? What happens after they're turned into a plant? Do they regret that? Do they enjoy the photosynthesis? Can they still reason? Do they still love? Do they still feel pain? And so on and so forth. Why won't we write a story on this? What happens after a human gets turned into a plant? How does that new species spread? Do they have plant sex?