chicago, The importance of trees: recent progress with understanding the history of plant life Professor Sir Peter Crane (University of Chicago, Illinois, USA) Summary: Much was learnt about plant evolution in the first 100 years following On the Origin of Species, but progress in recent decades has been equally rapid, especially with new approaches to develop and test different kinds of evolutionary trees that model the specific pathways of plant evolution. Such trees provide a basis for understanding how the major groups of living and fossil plants are interrelated, and in turn, this has opened up possibilities for research in many new areas. In this lecture, I will review our current understanding of the origin and early diversification of land plants, vascular plants, seed plants and flowering plants. In all four cases, many questions remain to be answered, but improved insights have come, most reliably, by integrating information from living and fossil plants towards the development of increasingly robust phylogenetic and stratigraphic patterns. Among living plants, the widespread application of phylogenetic techniques based on molecular sequence data, together with new studies of plant structure, function and development, have been especially influential. Among fossil plants, new perspectives continue to come from studies of recently discovered and classic localities, as well as from information obtained through the application of new techniques.