As a botanist (well, at least that is what the diploma says) one thing that you might think about is that you and your audience expect the 'natural' plants to have a familiar feel. That feel is mostly European with some subtropics thrown in. So as you look to make fantasy plants always be thinking about how you can tweak that just a bit to throw things off. An example: When I used to take freshman biology students into the north woods of Minnesota there was a part in the woods where for no reason at all there were a group of pines that had been planted in straight rows. They were the same size/age of their peers and best I could ever figure out they were planted that way at the whim of some bored national forestry guy as they filled in an area. *However* when I went to explain it I would reference a few plants that had stems at 90 degree angles and then launch into a spiel about how this primitive pine had the same thing going, but with its root system and that they produced suckers that would grow into new trees and *that* is why they grew at right angles to each other and thus in straight lines/lattices. Usually someone would call me out on it.

But imagine that on a map, here are a group of trees growing n a pattern, because that is how they grow - lines, Fibonacci curves, rings (ala toadstools), then give them a fantasy reason they grow that way - they grow in rings because they form minor gates to (fairyland, the abyss, the castle on the moor, etc) or they grow in lines because (and this is one I use) because there is one that is always two times larger than the others so that it gets struck by lightening which shoots from tree to tree for miles so that if you want to cross a tree line you always stop and look first to see if there is light flashing down (and up) the line.

I love this aspect of my campaign and my players do as well. Piers Anthony's Xanth series has a bunch of punny plants (shoe trees, pineapple trees with exploding fruit, etc.) , Niven's Integral Trees is about - trees in orbit, Tolkien's Ents (no entwives - so they only produce pollen?) and tons of others. Mapping some of it is tough on the continent/kingdom level but at the city/neighborhood level can be done.

If you would like to dig into this some more I have thought about this a great deal and think it is one of the most ignored aspects of fantasy literature/RPGs