Intelligence is an emotionally loaded word, but it is the tightest perimeter to define what they are doing. Couple of points: *Plant communication - not only root communication, they are somehow telling bug invasions to remote plants. Supposedly, it may be airborne hormones. They change the level of tanning in leaves to make catapillars away, and the level of torlalence is different among individuals *Social life - plants recognize their kin by light going through leaves. Using different channels to warn kind or others according to the level of danger. *Plant memory - they store memory, and accordingly learn. Within the generation, they change positions to capture full sun. Some vines even mimic surrounding plants' shape or colors. The capability may be explained in either way: sights or microorganisms.