This contribution demonstrates that the development and growth of plants depends on the success of complex communication processes. These communication processes are primarily sign-mediated interactions and are not simply an mechanical exchange of ‘information’, as that term has come to be understood (or misunderstood) in science. Rather, such interactions as I will be describing here involve the active coordination and organisation of a great variety of different behavioural patterns — all of which must be mediated by signs. Thus proposed, a biosemiotics of plant communication investigates communicationprocesses both within and among the cells, tissues, and organs of plants as sign-mediated interactions which follow (1) combinatorial (syntactic), (2) context-sensitive (pragmatic) and (3) content-specific (semantic) levels of rules. As will be seen in the cases under investigation, the context of interactionsin which a plant organism is interwoven determines the content arrangement of its response behaviour. And as exemplified by the multiply semiotic roles playedby the plant hormone auxin that I will discuss below, this means that a molecule type of identical chemical structure may function in the instantiation of differentmeanings (semantics) that are determined by the different contexts (pragmatics) in which this sign is used.