A lot of the plants aren't plants as we understand them (I bet none are).

And "plant" to us could be any organism that photosynthesizes and doesn't move much.Take kelp; most people think that kelp and marine red algae are plants, but they're actually photosynthetic colonial protists; they have no roots, no seeds, no leaves, no flowers, no stems, and they lack the reproductive structures of primitive plants such as mosses.

So the "plants" as they are defined on Pandora may be able to do quite a bit more, especially since they seem to have a nervous system.

They could be very complicated, as organisms, but there's no reason for them to implement complicated intelligence. An immobile organism doesn't have any reason to plan ahead or explicitly model what other creatures are thinking.

How so?

If I were an immobile organism, and I could do something that would benefit another organism while making the other organism tend to my needs, it would just be another form of symbiosis.

Did you know that cabbage plants exude pheromones when they are attacked by lepidopteran larvae?

The pheromones attract parasitoid wasps who lay their eggs on the caterpillar; the larvae maim the caterpillars as they eat them from the inside and ultimately kill most of the brood in the process.

The cabbage is saved from death by herbivory, the wasp finds hosts for its young, and the population of butterflies is regulated in the process. Even though the butterflies do not benefit, the control on the butterfly population helps regulate the equilibrium of surrounding ecosystems.

Modeling behavior and planning ahead are more complex, but the plants essentially have neurons, and that plus a large biomass opens a lot of doors.

I've always loved eating kelp and thinking, yeah, I'm eating protists. I also just discovered chrome doesn't know the word "protist" :P