This book surveys the momentous morphological change in plant evolution that created the terrestrial biosphere as we know it today. It takes as its premise that the study of plant evolution at its grandest is the study of how mutations in genes have changed the way the planet functions. The evolution of the leaf, for instance, change terrestrial carbon cycling and primary productivity, so changing the earth's atmosphere and the distribution of carbon. The book charts the rise to complexity of the three many organs systems of complex land plants, the axis or stem, the leaf, and the root. These organs system are surveyed morphologically in the light of empirical morphology, in which organ concepts are considered as hypotheses to be tested in a developmental, molecular, and phylogenetic framework. It also tackles the evolution of the seed (via heterospory and covering of the megasporangium) and the flower (by complex patterning of sporophylls and sterile phyllomes). All this is placed where possible in its molecular context, with the aim of demonstrating how evolving gene networks have given rise to increasing morphological complexity.