Are there any books that cover the flora of Galorion? I mean the relatively mundane stuff not the stuff that's sentient and wants to eat you. I suppose it would be possible to cobble together a picture from various info on alchemical reagents, poisons, drugs etc. but I was wondering if there was anything that covers plants with regards to habitat, cultural meanings and uses.
You can pull some information out of this thread, about trade goods: http://paizo.com/threads/rzs2oe8t?Trade-Routes-and-Trade-Goods-in-Golarion. It has some of what you're looking for (if you extrapolate grapes from wine, for example) and some suggestions of where to find the information.
Sorry I couldn't point you to a more concrete source.
Chapter 4 of the Inner Sea World Guide has a section on Flora of the Inner Sea that starts on page 255. I suspect there are other scattered sources, but that's a good place to start....and Pathfinder Wiki of course!