There are several forms of rapid plant movement which could be seen as intentional actions. (Let us leave aside their turning towards the sun and other tropism, taxis or kinesis, but temporarily grant them intentions). Why do these plants act? Sometimes to capture prey, like in the movie below. Sometimes to release seeds or pollen. The reasons for these movements are fairly obvious. To eat and reproduce. I think of these as practical actions, not gestures, since there is no intention to communicate.
Other plants seem to shy away or curl up their leaves in response to touch or other stimuli.
Dr. T. Ombrello – UCC Biology Department: “We can only guess as to why Mimosa pudica and a few other species have evolved to exhibit nyctinastic and seismonastic movements. It has been observed that folded and drooped leaves are not attractive to herbivores, and are often passed by in favor of more normal appearing leaves to eat. Also, folded and drooped leaves exchange less heat and water than fully expanded leaves, and this might have some survival value when the plants are under environmental stress.”
Although we may like to project our own shyness onto the plants behaviour, I do not think the plant is trying to appear modest. If it had legs it would probably flee, whatever impression that might leave behind. So, even if we grant a plant intentions it still doesn’t intend to communicate with the movements treated here. No plant gestures here I am afraid. Maybe we need better examples, anyone?