Nature generally has no trouble inspiring sci-fi or horror movies (Jaws, anyone?), but inspiration from the plant kingdom usually falls short; last time I checked, Swamp Thing and Little Shop of Horrors surely didn't improve with age.
The latest isn't scary, but it could inspire a sort of lyrical, moody film like Solaris. Henry Cowell State Park in California hosts the extremely rare albino redwood (perhaps as few as 28 specimens), and while they don't grow to great white hulks in the forest, they do spring ghost-like out of burls and nurse logs. Check it:
At the end of the video, simple park docents warn us that they're trusting us not to pluck albino redwoods. 'Trust' my foot: I'll bet they're haunted. Coming soon to a theater near you...