For the record I chose the scientific response as apposed to the metaphysical response because I do enough research in psionics with humans alone that I hardly have time to pay attention to theories on the plants role in the scheme. But I'll give you a quick taste of the theories my group has put forward:

Plants, have just as much a soul as the rest of us. The plants with the strongest souls are trees. Plants might be capable of communication with humans. Our rough theory states, however, that plants have a strange identity. It is a matrix of thought just as plants become a matrix of presence in the physical universe. In theory plants can and do hold a unique experience. This experience, however, is not stored directly with its ethereal presence. Rather, it is stored in the earth, along with the experience of every other plants on earth. It works sort of like a centralized processing computer with multiple terminals (if you have an understanding of computers this will bring things into full clarity). Basicly the terminal (plant) can interact with its user (life) store information unique to itself, and acquire data. However if you were to ask the terminal a question, it would be directed to the central processor (earth, sum of all plant life) for the answer. So if you asked a plant "Do you like being planted near the road" you would be answered with a consensus amongst all plants, and other earth oriented spirits in general. This is, however, wholly in theory and has not been independently verified, or verified in mass. The group I belong to is too busy working on attacks/defenses in psionics to worry about the nature of plants and their impact on the nature of psionics. They are, in fact, quite neutral.