INTRODUCTION

Flowering plants (angiosperms) comprise 250 000–300 000 living species and are more diverse than all other groups of extant plants combined. They dominate the vegetation over most of the Earth's land surface and therefore account for most of the primary productivity in terrestrial ecosystems. Despite their present-day importance, flowering plants were the last major group of land plants to appear in the fossil record. While all other major groups have an extensive fossil record that extends back to the Paleozoic or earliest Mesozoic, angiosperms have no well-established fossil record prior to the Cretaceous (Crane et al., 1995). The origin of flowering plants, and especially their rapid diversification during the Cretaceous and Tertiary, is therefore of great evolutionary interest and had profound consequences for the evolution of terrestrial ecosystems and the animals that inhabit them (Friis et al., 1987; Wing et al., 1992).

In this chapter we briefly introduce recent studies of angiosperm diversification, review the changing diversity of major plant groups through the Cretaceous, present new data on changing patterns of abundance, and briefly discuss the possible relationship between vegetational patterns and other aspects of Cretaceous global environmental change. While there is currently no clear evidence that the diversification of flowering plants was triggered by changes in the global environment, several patterns of vegetational change during the mid Cretaceous correlate broadly with major environmental perturbations including oceanic anoxia, increased tectonic activity and rapid sea floor spreading.