The BBC has a video up today showing how certain plant species communicate with other individual plants by releasing a gas when attacked, triggering the other plants to begin producing a toxin to ward off predators. The video illustrates this phenomenon with Arabidopsis plants, although the video implies that other plants do this as well.
BBC News - How plants warn each other of danger (ht: reddit)
The use of the word "language" to describe this phenomenon is certainly a stretch, but maybe it isn't any more of a stretch than using the word "language" to describe the scent-based communication system of ants. Since we usually spend a day on animal communication in our intro Linguistics courses, I think it'd be fun to include a couple of minutes on plant communication as well.
