XVI International Botanical Congess

Almost all photosynthesis on land is carried out by photosynthetic shoots, i.e. organs which are erect and branched and which obtain CO2 from the atmosphere and also absorb solar radiation. In turn, most of this photosynthesis is performed by homoiohydric shoots of embryophyte sporophytes, with most of the photosynthesis occurring in determinate structures in the shoot. The morphology of the shoot is an evolutionary compromise between light interception, CO2 uptake and the radiation balance of the photosynthetic structures, reproductive requirements, and the structural, ontogenetic and physiological constraints on the size and shape of the shoot. A further constraint on shoot physiology is the requirement that products of root-derived solutes and of photosynthates shall not result in materials which cannot be accumulated, re-exported to roots or secreted. We shall consider how the diversity of shoot structures relates to these constraints.