At a time when the popular perception of paleontology is dominated by images of dinosaurs and other spectacular vertebrates, or the mysteries surrounding the Cambrian “explosion” of animal life, it is perhaps not surprising that the rich and informative fossil record of plants has scarcely made an impact on the public consciousness. In reality, as one would expect from those organisms that comprise the bulk of the biological material in terrestrial ecosystems, the fossil record of plants is extensive (Stewart and Rothwell, 1993). Leaves, wood fragments, pollen grains, spores, fruits, seeds and other plant parts are the most common fossils in rocks deposited in ancient flood plains, lakes and many other environments - and they are often exquisitely preserved. This excellent fossil record provides important information about the ecology of ancient terrestrial ecosystems. The quality of the plant fossil record also makes paleobotanical data highly informative about the historical pattern of plant evolution. It is this pattern, and its congruence with patterns in the characters of living and fossil plants — as summarized in a classification — that is the focus of this chapter.