Old-man-gator has a really brilliant idea that seems to have been overlooked:
Certain plants could absolutely depend on certain minerals, types of soil, rock types, whatever, while others would simply grow better or worse, depending on the geologic conditions, and modified by climate and moisture presence, as defined in the Raws.
If plant and fungal life/growth and diversification could be linked to the type/types of stone in a given area, as well as to climate, and if then, animals and their diversification could be linked-generally or specifically-to the types of plants in a given area, starting with vermin and moving on up, we could end up with a biosphere which actually made sense, and which might then sustain itself outside of direct Dev control.
You could then, sensically, include extremely specific plant and fungal life, such as a mushroom that will only grow on iron ore, a mold that only grows in the presence of cinnabar, or a glowing lichen that must be sown only on rocks with a high phospherous content.
Not only could these be used as identifiers as to what our miners could expect to find in an area, but such plants might validly be extracted for special substances like poisons, acids, etc.
Our dwarfs could also intentionally sow plants in an area, in an effort to attract specific vermin, or larger creatures.
Vermin-in game terms-might even spawn from certain specific plants, or types of plants.
If all of this were done, it could serve to make plants-taken as a whole-absolutely vital to the game, instead of just making a few of them exploitable.