I got my hands on a really evil Shadowrun sourcebook: Parabotany. Yes, it's all plants, mutated, awakened/magical and fairly normal ones. And no-one ever expects plants to be anything else than scenery. Most of the plants are fairly harmless or even useful, especially for an awakened character. But some can get characters in serious trouble. Most plants I have seen used by GMs (mostly in fantasy games) are half-sentient and I'm not a fan of this.
Plants are quite awesome the way they are, not intelligent but well-prepared for survival with a bag of tricks we ignore at our own risk. Plants communicate. Plants fight and plants move. So you pick some salad for a meal and suddenly the rest of the salad turns poisonous because the first plants gives off a chemical signal 'I'm being attacked!'? Plants that use you as an unwilling seed carrier, maybe by lodging sharp seeds in your skin, all the plants in the area at once? Plants that can call animals that protect them when they are being picked or trampled? Plants do all that. Now let's ramp it up, add some magic to the mix and the lush meadow your character is walking through suddenly is a battlefield.
I have some favourites from the Parabotany and State of the Art sourcebooks, like the giant tumbleweed and the perfectly harmless looking grass with seeds that will shatter on contact, capable of sandblasting a car or person. My players are already a bit paranoid about the animals they encounter during their roadtrip. By the time they reach Boston, they will probably twitch nervously at the sight of a tuft of grass.