The functional significance of leaf structure: a search for generalizations

The coupling between leaf structure and function is illustrated with refere nce to two examples, the C-4 photosynthetic pathway and leaf pubescence. A distinction is made between function and functional significance. The latte r is defined as the role, significance or consequence of a structure, where as the former is more simply the action that a structure is capable of perf orming. Using the two examples, four generalizations are made concerning th e relationships between structure, function and functional significance: th e functional significance of leaf structure is environment-dependent; the r elationship between functional significance and structure is sometimes non- intuitive; functional equivalency means that there is often more than one ' solution' to the same 'constraint'; and the consequences of leaf structure can exert profound effects at levels of organization beyond those of the in dividual organism and may play a critical role in determining community str ucture and function, through interactions with other species and trophic le vels. The importance of understanding the consequences in variation in leaf structure at the global scale is illustrated with reference to the issue o f global climate change.