4 ideas
First-generation colonists fleeing Earth settle on Pax, where some plants are poisonous and some colonists die. Over later generations the bamboo, named Stevland, learns to exchange written symbols with the humans, and the colony eventually admits it as a citizen of their community.
A plant that cannot move or speak can still communicate by changing the chemistry of what it offers. It can make fruit nourishing, addictive, or toxic depending on what an animal does. Feeding becomes a form of training, so the plant shapes the behavior of mobile creatures the way a trainer uses treats and shocks.
Colonists who think they are cultivating the local plants are also being cultivated. The plants select which humans thrive and which habits persist by controlling the food supply. Seen this way, agriculture is a mutual taming in which it is unclear which species is the farmer.
Humans and a radically alien intelligence cannot share a mind or fully trust each other's motives. Because the plant's lifespan and timescale far exceed a human life, each human generation must inherit, test, and renegotiate the terms its predecessors set.