As plants clearly attract most attention it sounds like a good idea to start thinking up some plants that might do well in certain tempretures ranges.
It is quite likely that a lot of plants will have to be traded. And it might be better if we get rid of the seasons thing and replace it by tempreture only (you can still select what plant grows when). This would mean that if I want to grow pig tail all year round I can do that.
Now some plants:
Magma root: A plant that need extreme heat produces a very high quility food.
Snowbery: A plant that only grow in very cold areas producies snowberies a medium quility food and usable for white dye.
Cave grass:Plant that grows in almost all conditions. Can be milled to make a very low quility food and can be used for low quility fibers.
Bat leaf: A black leafed plant that does best in medium tempreture caves, used to make black dye.
Caveman wheat: A wheat that grows in slightly high tempreture caves, Can be milled to make a high quility and high amout of food.
Heatbite: A rare plant which produces a small amout of heat lives in very high tempreture areas, Can be made into poison when it's implented.
Lead berries: Plant that grows in low tempreture areas can be used to make dye.
You should think about what alcohols those make aswell. Like evercold wine or something for snowbery. Which would be nearly as good as sunshine, cause everybody likes their alcohol cold. And something equally as valuable for magma root because it would take a bit of work to get so the value should reflect that effort. Though maybe it would make dwarfs more happy to eat it then to drink it, cause of its properties.