In regards to DF talk 16, just a few thoughts the on how the "deadly plant" topic could work.
Really simple savage plant, a 'Venus Dorf Trap', could be classified as a creature, but act as if it were attached to a tile (like a chained animal). It could move around it's 3x3 plot, and attack those around it.
Another type could just be inconspicuous shrubbery, which could release gasses or secretions, with certain effects, whenever trampled or picked. (could apply to evil biomes as well, and you could restrict certain effects to certain biomes. [A savage shrub could cause blisters, evil shrubs could cause rot/death, joyfull shrubs could heal/explode]. Perhaps secretions could be carefully collected, and be worked into adventure mode alchemy/magic)
There could also be the simple "lash/grab" trees, that would have a basic attack. Once grabbing, dragging is implemented, you could have creeping vines that try to drag the player to certain areas (Dorf Trap nests), and can be worked into the multi z-level tree idea, with vines coming down to strangle/lift the player into the foliage death-pit, with the player hacking away at trees and vines, hoping the fall isn't too high.
There could also be projectile plants, that could shoot just straight barbs to do damage, or include terrible afflictions.
On a related note, being able to change the immediate environment would be cool. (digging shallow holes [until better skilled/equipped], chopping down trees [or bloodthirsty vines])