Observed form can be proposed to be the result of interacting constraints and demands. Historical factors (phylogenetic constraints) determine the range of structural features from which novel forms can evolve, while developmental constraints influence which of all possible novel forms will be feasible in the genetic environment in which they are expressed. Environmental factors interact with morphology at different scales - the relationship of growth form to life strategy and the physical and temporal exploitation of environmental resources, and the role of form in mediating the interaction between physiology and the environment through water & mineral capture, desiccation tolerance and gas exchange. In this symposium a selection of these interacting elements will be explored.

Key words: bryophytes, constraints, development, morphology, physiology