If this thread is going to be something major, I'd like to at least request a link to the
Improved Farming thread, which has had a very long and serious discussion about farming.
Frankly, I don't think there's much need to be talking about different kinds of food plants so much...
I mean, really, would you be able to tell the difference in terms of game code between tubers and vine plants when it comes to farming as it is currently implimented? We could mod in more plants now, but there really isn't much point, as there isn't any need for any sort of nutritional balance, and the only functional differences between one plant and another as far as food goes is that foods like quarry bushes and sweet pods provide five times the food of other plants, and are, hence, innately superior as a food product, with all others being simply there for a little variety or the textile industry. This means that you can put in your marshmallows right now if you really wanted to, but if we are going to actually want more diversity in our foodstuffs as part of the vanilla game, what we really need is the coding to actually make the diversity matter. That means either differences in the soil types that are required to grow those plants, or differences in nutritional values, which would be in one of the several "nutrition" threads.
I don't think that poisonous plants would be hard to make right now, although I haven't worked with those any, so long as you just make the flesh of the plant out of a material that gives symptoms. The main problem with this is the need to be able to
apply the poisons, which can be presumed to be in the works. (Thorny plants can also be similarly implimented.)
Weeds are a suggestion heavily explored in the Improved Farming thread, with their potential use as a means of increasing the amount of labor one must place into the fields. (Of course, this was before animals all but exploded with meat at the slightest touch...)
Growing trees are likewise a back-burner issue of Toady's, as it's a stated goal, and presumably, fruit-bearing trees should come along with that, since it's certainly been suggested often enough. I think the problem with that stems from the odd way that all plants on farms are destroyed at the end of a year as part of the way that farms are programmed (which may, itself, be a stop-gap to a different problem), but that's pretty much just speculation on my part.
Ornamental plants are also linked to the above problem. We'd really only need to have a means of making plants (flowers) count as a decoration to a room when in full bloom, and have them be seasonal to make that work. (I also put that in the
Pimp My Fort thread.)
Carnivorous trees, carnivorous plants, anthropromorphic trees etc. all can fall under a category of "creates a creature" plants, which are something people (myself included) have tried doing using things like the reactions mods. If Toady would want to do it directly, that's great, but it might come to us faster through the reaction method, if Toady ever wants to let the modders have their "golem mods".
edit: expanding third paragraph.